ORCID Profile
0000-0003-0598-7425
Current Organisation
Centre National de la Recherche Scientifique
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Publisher: American Chemical Society (ACS)
Date: 23-06-2022
Abstract: In the framework of the computational determination of highly accurate vertical excitation energies in small organic compounds, we explore the possibilities offered by the equation-of-motion formalism relying on the approximate fourth-order coupled-cluster (CC) method, CC4. We demonstrate, using an extended set of more than 200 reference values based on CC including up to quadruples excitations (CCSDTQ), that CC4 is an excellent approximation to CCSDTQ for excited states with a dominant contribution from single excitations with an average deviation as small as 0.003 eV. We next assess the accuracy of several additive basis set correction schemes, in which vertical excitation energies obtained with a compact basis set and a high-order CC method are corrected with lower-order CC calculations performed in a larger basis set. Such strategies are found to be overall very beneficial, though their accuracy depends significantly on the actual scheme. Finally, CC4 is employed to improve several theoretical best estimates of the QUEST database for molecules containing between four and six (nonhydrogen) atoms, for which previous estimates were computed at the CCSDT level.
Publisher: American Physical Society (APS)
Date: 19-05-2010
Publisher: American Chemical Society (ACS)
Date: 18-11-2021
Publisher: American Chemical Society (ACS)
Date: 20-03-2019
DOI: 10.26434/CHEMRXIV.7868351.V1
Abstract: P T -symmetry — invariance with respect to combined space reflection P and time reversal T — provides a weaker condition than (Dirac) Hermiticity for ensuring a real energy spectrum of a general non-Hermitian Hamiltonian. PT -symmetric Hamiltonians therefore form an intermediate class between Hermitian and non-Hermitian Hamiltonians. In this work, we derive the conditions for PT-symmetry in the context of electronic structure theory, and specifically, within the Hartree–Fock (HF) approximation. We show that the HF orbitals are symmetric with respect to the P T operator if and only if the effective Fock Hamiltonian is PT -symmetric, and vice versa. By extension, if an optimal self-consistent solution is invariant under PT , then its eigenvalues and corresponding HF energy must be real. Moreover, we demonstrate how one can construct explicitly PT -symmetric Slater determinants by forming PT doublets (i.e. pairing each occupied orbital with its PT -transformed analogue), allowing PT -symmetry to be conserved throughout the self-consistent process. Finally, considering the H2 molecule as an illustrative ex le, we observe PT-symmetry in the HF energy landscape and find that the symmetry-broken unrestricted HF wave functions (i.e. diradical configurations) are P T -symmetric, while the symmetry-broken restricted HF wave functions (i.e. ionic configurations) break PT -symmetry.
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0FD90026E
Publisher: Elsevier BV
Date: 04-2007
Publisher: AIP Publishing
Date: 09-09-2021
DOI: 10.1063/5.0060698
Abstract: In single-reference coupled-cluster (CC) methods, one has to solve a set of non-linear polynomial equations in order to determine the so-called litudes that are then used to compute the energy and other properties. Although it is of common practice to converge to the (lowest-energy) ground-state solution, it is also possible, thanks to tailored algorithms, to access higher-energy roots of these equations that may or may not correspond to genuine excited states. Here, we explore the structure of the energy landscape of variational CC and we compare it with its (projected) traditional version in the case where the excitation operator is restricted to paired double excitations (pCCD). By investigating two model systems (the symmetric stretching of the linear H4 molecule and the continuous deformation of the square H4 molecule into a rectangular arrangement) in the presence of weak and strong correlations, the performance of variational pCCD (VpCCD) and traditional pCCD is gauged against their configuration interaction (CI) equivalent, known as doubly occupied CI, for reference Slater determinants made of ground- or excited-state Hartree–Fock orbitals or state-specific orbitals optimized directly at the VpCCD level. The influence of spatial symmetry breaking is also investigated.
Publisher: Informa UK Limited
Date: 09-2013
Publisher: AIP Publishing
Date: 10-11-2020
DOI: 10.1063/5.0028040
Abstract: We discuss the physical properties and accuracy of three distinct dynamical (i.e., frequency-dependent) kernels for the computation of optical excitations within linear response theory: (i) an a priori built kernel inspired by the dressed time-dependent density-functional theory kernel proposed by Maitra et al. [J. Chem. Phys. 120, 5932 (2004)], (ii) the dynamical kernel stemming from the Bethe–Salpeter equation (BSE) formalism derived originally by Strinati [Riv. Nuovo Cimento 11, 1–86 (1988)], and (iii) the second-order BSE kernel derived by Zhang et al. [J. Chem. Phys. 139, 154109 (2013)]. The principal take-home message of the present paper is that dynamical kernels can provide, thanks to their frequency-dependent nature, additional excitations that can be associated with higher-order excitations (such as the infamous double excitations), an unappreciated feature of dynamical quantities. We also analyze, for each kernel, the appearance of spurious excitations originating from the approximate nature of the kernels, as first evidenced by Romaniello et al. [J. Chem. Phys. 130, 044108 (2009)]. Using a simple two-level model, prototypical ex les of valence, charge-transfer, and Rydberg excited states are considered.
Publisher: AIP Publishing
Date: 15-06-2022
DOI: 10.1063/5.0089317
Abstract: By recasting the non-linear frequency-dependent GW quasiparticle equation into a linear eigenvalue problem, we explain the appearance of multiple solutions and unphysical discontinuities in various physical quantities computed within the GW approximation. Considering the GW self-energy as an effective Hamiltonian, it is shown that these issues are key signatures of strong correlation in the (N ± 1)-electron states and can be directly related to the intruder state problem. A simple and efficient regularization procedure inspired by the similarity renormalization group is proposed to avoid such issues and speed up the convergence of partially self-consistent GW calculations.
Publisher: American Chemical Society (ACS)
Date: 02-07-2019
Abstract: Considering 41 electronic transitions in small- and medium-sized organic molecules, we benchmark the performances of 36 hybrid functionals within time-dependent density-functional theory (TD-DFT) and nine wave function theory (WFT) methods [CCSDT, CC3, CCSDT-3, CCSDR(3), CCSD, CC2, ADC(3), ADC(2), and SOS-ADC(2)]. Compared to highly accurate experimental 0-0 energies, it turns out that all coupled cluster (CC) approaches that include contributions from the triples [i.e., CCSDT, CC3, CCSDT-3 and CCSDR(3)] deliver a root-mean-square error (RMSE) smaller than or equal to 0.05 eV. The remaining WFT methods [i.e., CCSD, CC2, ADC(3), ADC(2), and SOS-ADC(2)] yield larger deviations with RMSE lying between 0.11 and 0.27 eV. Irrespective of the exchange-correlation functional, TD-DFT yields larger deviations (RMSE ⩾ 0.30 eV). For vertical transitions without clear experimental equivalents (such as vertical absorption and fluorescence), a comparison between TD-DFT and CC3 provides a globally unchanged ranking of the various functionals. However, the errors on emission energies tend to be larger than on absorption energies, hinting that studying the latter property is not sufficient to gain a complete view of TD-DFT's performances. Finally, by cross-comparisons between TD-DFT and WFT, we observe that the WFT method selected as reference significantly impacts the conclusions regarding the overall accuracy of a given exchange-correlation functional. For ex le, for vertical absorption energies, the "best" functional is TPSSh (RMSE = 0.29 eV) based on CC3 reference energies, while LC-ωPBE (RMSE = 0.12 eV) is superior to the other functionals when one considers ADC(3) as the reference method.
Publisher: American Physical Society (APS)
Date: 30-05-2014
Publisher: American Chemical Society (ACS)
Date: 05-06-2019
Abstract: PT-symmetry-invariance with respect to combined space reflection P and time reversal T-provides a weaker condition than (Dirac) Hermiticity for ensuring a real energy spectrum of a general non-Hermitian Hamiltonian. PT-symmetric Hamiltonians therefore form an intermediate class between Hermitian and non-Hermitian Hamiltonians. In this work, we derive the conditions for PT-symmetry in the context of electronic structure theory and, specifically, within the Hartree-Fock (HF) approximation. We show that the HF orbitals are symmetric with respect to the PT operator
Publisher: American Chemical Society (ACS)
Date: 28-01-2019
Abstract: Excited states exhibiting double-excitation character are notoriously difficult to model using conventional single-reference methods, such as adiabatic time-dependent density functional theory (TD-DFT) or equation-of-motion coupled cluster (EOM-CC). In addition, these states are typical experimentally "dark", making their detection in photoabsorption spectra very challenging. Nonetheless, they play a key role in the faithful description of many physical, chemical, and biological processes. In the present work, we provide accurate reference excitation energies for transitions involving a substantial amount of double excitation using a series of increasingly large diffuse-containing atomic basis sets. Our set gathers 20 vertical transitions from 14 small- and medium-size molecules (acrolein, benzene, beryllium atom, butadiene, carbon dimer and trimer, ethylene, formaldehyde, glyoxal, hexatriene, nitrosomethane, nitroxyl, pyrazine, and tetrazine). Depending on the size of the molecule, selected configuration interaction (sCI) and/or multiconfigurational (CASSCF, CASPT2, (X)MS-CASPT2, and NEVPT2) calculations are performed in order to obtain reliable estimates of the vertical transition energies. In addition, coupled cluster approaches including at least contributions from iterative triples (such as CC3, CCSDT, CCSDTQ, and CCSDTQP) are assessed. Our results clearly evidence that the error in CC methods is intimately related to the amount of double-excitation character of the transition. For "pure" double excitations (i.e., for transitions which do not mix with single excitations), the error in CC3 can easily reach 1 eV, while it goes down to a few tenths of an electronvolt for more common transitions (such as in trans-butadiene) involving a significant amount of singles. As expected, CC approaches including quadruples yield highly accurate results for any type of transition. The quality of the excitation energies obtained with multiconfigurational methods is harder to predict. We have found that the overall accuracy of these methods is highly dependent on both the system and the selected active space. The inclusion of the σ and σ* orbitals in the active space, even for transitions involving mostly π and π* orbitals, is mandatory in order to reach high accuracy. A theoretical best estimate (TBE) is reported for each transition. We believe that these reference data will be valuable for future methodological developments aiming at accurately describing double excitations.
Publisher: American Physical Society (APS)
Date: 08-06-2011
Publisher: American Chemical Society (ACS)
Date: 22-12-2022
Publisher: American Physical Society (APS)
Date: 18-01-2023
Publisher: American Chemical Society (ACS)
Date: 08-01-2020
DOI: 10.1021/ACS.JPCLETT.9B03652
Abstract: The search for new models rapidly delivering accurate excited-state energies and properties is one of the most active research lines of theoretical chemistry. Along with these developments, the performance of known methods is constantly reassessed on the basis of new benchmark values. In this Letter, we show that the third-order algebraic diagrammatic construction, ADC(3), does not yield transition energies of the same quality as the third-order coupled cluster method, CC3. This is demonstrated by extensive comparisons with several hundred high-quality vertical transition energies obtained with FCI, CCSDTQ, and CCSDT. Direct comparisons with experimental 0-0 energies of small- and medium-size molecules support the same conclusion, which holds for both valence and Rydberg transitions. Considering these results, we introduce a composite approach, ADC(2.5), which consists of averaging the ADC(2) and ADC(3) excitation energies. Although ADC(2.5) does not match the CC3 accuracy, it significantly improves the ADC(3) results, especially for vertical energies.
Publisher: American Chemical Society (ACS)
Date: 22-09-2023
Publisher: AIP Publishing
Date: 28-04-2013
DOI: 10.1063/1.4802589
Abstract: We introduce a new paradigm for one-dimensional uniform electron gases (UEGs). In this model, n electrons are confined to a ring and interact via a bare Coulomb operator. We use Rayleigh-Schrödinger perturbation theory to show that, in the high-density regime, the ground-state reduced (i.e., per electron) energy can be expanded as \\documentclass[12pt]{minimal}\\begin{document}$\\epsilon (r_s,n) = \\epsilon _0(n) r_s^{-2} + \\epsilon _1(n) r_s^{-1} + \\epsilon _2(n) +\\epsilon _3(n) r_s\\break + \\cdots\\,$\\end{document}ε(rs,n)=ε0(n)rs−2+ε1(n)rs−1+ε2(n)+ε3(n)rs+⋯, where rs is the Seitz radius. We use strong-coupling perturbation theory and show that, in the low-density regime, the reduced energy can be expanded as \\documentclass[12pt]{minimal}\\begin{document}$\\epsilon (r_s,n) = \\eta _0(n) r_s^{-1} + \\eta _1(n) r_s^{-3/2}\\break + \\eta _2(n) r_s^{-2} + \\cdots\\,$\\end{document}ε(rs,n)=η0(n)rs−1+η1(n)rs−3/2+η2(n)rs−2+⋯. We report explicit expressions for ε0(n), ε1(n), ε2(n), ε3(n), η0(n), and η1(n) and derive the thermodynamic (large-n) limits of each of these. Finally, we perform numerical studies of UEGs with n = 2, 3, …, 10, using Hylleraas-type and quantum Monte Carlo methods, and combine these with the perturbative results to obtain a picture of the behavior of the new model over the full range of n and rs values.
Publisher: American Chemical Society (ACS)
Date: 23-03-2007
DOI: 10.1021/CT6003214
Abstract: Among all the Quantum Mechanics/Molecular Mechanics (QM/MM) methods available to describe large molecular systems, the Local Self-Consistent Field/MM (LSCF/MM) one uses frozen doubly occupied Strictly Localized Bonding Orbital (SLBO) to connect the QM fragment to the one treated at the MM level. This approach is correct as long as the QM part is large enough to minimize the artifacts that could arise because of the fixed SLBO. If one wants to decrease the size of the QM subsystem, one clearly needs to help the SLBO to relax according to the variations of the global wave function. Also, the SLBO have to adjust itself according to the modification of the surrounding if we want to improve the method. Here, we present a modification of the original LSCF method called Optimized LSCF (OLSCF) where each SLBO is allowed to mix with its corresponding Strictly Localized Anti Bonding Orbital (SLABO) resulting in an adjustment of the two-electron bond described by a self-consistent SLBO (SCSLBO). We test the new methodology against the modification of the QM part (internal perturbation) and against the variation of the surroundings (external perturbation) represented either by a dielectric continuum or by a classical point charge. In each case the initial SLBO is the symmetric C-C SLBO of the ethane molecule. It is shown that the optimized SCSLBO presents a final polarity in perfect agreement with what could be expected as the result of a reaction to the internal or external perturbation.
Publisher: AIP Publishing
Date: 05-02-2016
DOI: 10.1063/1.4940919
Abstract: Natural orbitals (NOs) are central constituents for evaluating correlation energies through efficient approximations. Here, we report the closed-form expression of the NOs of two-electron quantum rings, which are prototypical finite-extension systems and new starting points for the development of exchange-correlation functionals in density functional theory. We also show that the natural occupation numbers for these two-electron paradigms are in general non-vanishing and follow the same power law decay as atomic and molecular two-electron systems.
Publisher: American Physical Society (APS)
Date: 21-09-2011
Publisher: American Chemical Society (ACS)
Date: 07-05-2020
Publisher: American Chemical Society (ACS)
Date: 28-08-2019
DOI: 10.26434/CHEMRXIV.9733607.V1
Abstract: The NO method for static correlation is combined with second-order Mller-Plesset perturbation theory (MP2) and coupled-cluster singles and doubles (CCSD) to account for dynamic correlation. The MP2 and CCSD expressions are adapted from nite-temperature CCSD, which includes orbital occupancies and vacancies, and expanded orbital summations. Correlation is partitioned with the aid of d ing factors incorporated into the MP2 and CCSD residual equations. Potential energy curves for a selection of diatomics are in good agreement with extrapolated full conguration interaction results (exFCI), and on par with conventional multireference approaches.
Publisher: American Chemical Society (ACS)
Date: 27-01-2018
Abstract: In diffusion Monte Carlo (DMC) methods, the nodes (or zeroes) of the trial wave function dictate the magnitude of the fixed-node (FN) error. In standard DMC implementations, the nodes are optimized by stochastically optimizing a short multideterminant expansion in the presence of an explicitly correlated Jastrow factor. Here, following a recent proposal, we pursue a different route and consider the nodes of selected configuration interaction (sCI) expansions built with the CIPSI (Configuration Interaction using a Perturbative Selection made Iteratively) algorithm. By increasing the size of the sCI expansion, these nodes can be systematically and deterministically improved. The present methodology is used to investigate the properties of the transition metal sulfide molecule FeS. This apparently simple molecule has been shown to be particularly challenging for electronic structure theory methods due to the proximity of two low-energy quintet electronic states of different spatial symmetry and the difficulty to treat them on equal footing from a one-electron basis set point of view. In particular, we show that, at the triple-ζ basis set level, all sCI results-including those extrapolated at the full CI (FCI) limit-disagree with experiment, yielding an electronic ground state of
Publisher: American Physical Society (APS)
Date: 21-07-2011
Publisher: AIP Publishing
Date: 28-01-2019
DOI: 10.1063/1.5085121
Abstract: Processes related to electronically excited states are central in many areas of science however, accurately determining excited-state energies remains a major challenge in theoretical chemistry. Recently, higher energy stationary states of non-linear methods have themselves been proposed as approximations to excited states, although the general understanding of the nature of these solutions remains surprisingly limited. In this letter, we present an entirely novel approach for exploring and obtaining excited stationary states by exploiting the properties of non-Hermitian Hamiltonians. Our key idea centres on performing analytic continuations of conventional quantum chemistry methods. Considering Hartree-Fock theory as an ex le, we analytically continue the electron-electron interaction to expose a hidden connectivity of multiple solutions across the complex plane, revealing a close resemblance between Coulson-Fischer points and non-Hermitian degeneracies. Finally, we demonstrate how a ground-state wave function can be morphed naturally into an excited-state wave function by constructing a well-defined complex adiabatic connection.
Publisher: American Chemical Society (ACS)
Date: 13-09-2018
Abstract: We report unphysical irregularities and discontinuities in some key experimentally measurable quantities computed within the GW approximation of many-body perturbation theory applied to molecular systems. In particular, we show that the solution obtained with partially self-consistent GW schemes depends on the algorithm one uses to self-consistently solve the quasiparticle (QP) equation. The main observation of the present study is that each branch of the self-energy is associated with a distinct QP solution and that each switch between solutions implies a significant discontinuity in the quasiparticle energy as a function of the internuclear distance. Moreover, we clearly observe "ripple" effects, i.e., when a discontinuity in one of the QP energies induces (smaller) discontinuities in the other QP energies. Going from one branch to another implies a transfer of weight between two solutions of the QP equation. The cases of occupied, virtual, and frontier orbitals are separately discussed on distinct diatomics. In particular, we show that multisolution behavior in frontier orbitals is more likely if the HOMO-LUMO gap is small.
Publisher: American Chemical Society (ACS)
Date: 13-05-2019
Abstract: Quantum chemistry is a discipline which relies heavily on very expensive numerical computations. The scaling of correlated wave function methods lies, in their standard implementation, between
Publisher: American Physical Society (APS)
Date: 23-02-2012
Publisher: Elsevier BV
Date: 11-2010
Publisher: Elsevier BV
Date: 08-2006
Publisher: Wiley
Date: 05-03-2010
DOI: 10.1002/QUA.22072
Publisher: American Chemical Society (ACS)
Date: 16-04-2020
Publisher: AIP Publishing
Date: 26-04-2022
DOI: 10.1063/5.0088364
Abstract: While the well-established GW approximation corresponds to a resummation of the direct ring diagrams and is particularly well suited for weakly correlated systems, the T-matrix approximation does sum ladder diagrams up to infinity and is supposedly more appropriate in the presence of strong correlation. Here, we derive and implement, for the first time, the static and dynamic Bethe–Salpeter equations when one considers T-matrix quasiparticle energies and a T-matrix-based kernel. The performance of the static scheme and its perturbative dynamical correction are assessed by computing the neutral excited states of molecular systems. A comparison with more conventional schemes as well as other wave function methods is also reported. Our results suggest that the T-matrix-based formalism performs best in few-electron systems where the electron density remains low.
Publisher: American Chemical Society (ACS)
Date: 07-03-2008
DOI: 10.1021/CT700188W
Abstract: The geometries and UV-vis spectra of azobenzene dyes grafted as a side chain on poly(l-glutamic acid) have been investigated using a combination of quantum mechanics/molecular mechanics (QM/MM) and time-dependent density functional theory (TD-DFT) methods at the TD-PBE0/6-311+G(d,p)//B3LYP/6-311G(d,p):Amber ff99 level of theory. The influence of the secondary structure of the polypeptide on the electronic properties of both the trans and cis conformations of azobenzene dyes has been studied. It turns out that the grafted dyes exhibit a red-shift of the π → π* absorption energies mainly due to the auxochromic shift induced by the peptidic group used to link the chromophoric unit to the polypeptide and that specific interactions between the glutamic side chain and the azobenzene moiety lead to a large blue-shift of the n → π* transition.
Publisher: American Chemical Society (ACS)
Date: 15-05-2019
DOI: 10.1021/ACS.JPCLETT.9B01176
Abstract: We report a universal density-based basis-set incompleteness correction that can be applied to any wave function method. This correction, which appropriately vanishes in the complete basis-set (CBS) limit, relies on short-range correlation density functionals (with multideterminant reference) from range-separated density-functional theory (RS-DFT) to estimate the basis-set incompleteness error. Contrary to conventional RS-DFT schemes that require an ad hoc range-separation parameter μ, the key ingredient here is a range-separation function μ(r) that automatically adapts to the spatial nonhomogeneity of the basis-set incompleteness error. As illustrative ex les, we show how this density-based correction allows us to obtain CCSD(T) atomization and correlation energies near the CBS limit for the G2 set of molecules with compact Gaussian basis sets.
Publisher: AIP Publishing
Date: 14-02-2013
DOI: 10.1063/1.4790613
Abstract: We show that the expression of the high-density (i.e., small-rs) correlation energy per electron for the one-dimensional uniform electron gas can be obtained by conventional perturbation theory and is of the form εc(rs) = −π2/360 + 0.00845 rs + …, where rs is the average radius of an electron. Combining these new results with the low-density correlation energy expansion, we propose a local-density approximation correlation functional, which deviates by a maximum of 0.1 mhartree compared to the benchmark diffusion Monte Carlo calculations.
Publisher: AIP Publishing
Date: 22-12-2014
DOI: 10.1063/1.4903984
Abstract: We introduce a new basis function (the spherical Gaussian) for electronic structure calculations on spheres of any dimension D. We find general expressions for the one- and two-electron integrals and propose an efficient computational algorithm incorporating the Cauchy-Schwarz bound. Using numerical calculations for the D = 2 case, we show that spherical Gaussians are more efficient than spherical harmonics when the electrons are strongly localized.
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0FD90024A
Publisher: American Chemical Society (ACS)
Date: 25-03-2022
Abstract: Methods able to simultaneously account for both static and dynamic electron correlations have often been employed, not only to model photochemical events but also to provide reference values for vertical transition energies, hence allowing benchmarking of lower-order models. In this category, both the complete-active-space second-order perturbation theory (CASPT2) and the
Publisher: Frontiers Media SA
Date: 29-10-2021
DOI: 10.3389/FCHEM.2021.751054
Abstract: Using the simple (symmetric) Hubbard dimer, we analyze some important features of the GW approximation. We show that the problem of the existence of multiple quasiparticle solutions in the (perturbative) one-shot GW method and its partially self-consistent version is solved by full self-consistency. We also analyze the neutral excitation spectrum using the Bethe-Salpeter equation (BSE) formalism within the standard GW approximation and find, in particular, that 1) some neutral excitation energies become complex when the electron-electron interaction U increases, which can be traced back to the approximate nature of the GW quasiparticle energies 2) the BSE formalism yields accurate correlation energies over a wide range of U when the trace (or plasmon) formula is employed 3) the trace formula is sensitive to the occurrence of complex excitation energies (especially singlet), while the expression obtained from the adiabatic-connection fluctuation-dissipation theorem (ACFDT) is more stable (yet less accurate) 4) the trace formula has the correct behavior for weak ( i.e. , small U ) interaction, unlike the ACFDT expression.
Publisher: American Chemical Society (ACS)
Date: 30-04-2009
DOI: 10.1021/CT900093H
Abstract: Hybrid QM/MM calculations were performed on a circular macropeptide (kalata B1, PDB ID 1NB1) containing three disulfide linkages, to evaluate their respective reactivities toward (gas-phase) electron valence-attachment of one and two electron(s). The three disulfide bonds -CH2-S-S-CH2- were simultaneously described at the MP2/6-31+G**(S),6-31G*(C,H) level of theory, and the remaining of the 29 residues of kalata B1 were described by the CHARMM27 force field. The one-electron addition is favored on the linkage between cysteine residues 1 and 15, Cys(1-15), by ca. 1 eV over the two other disulfide linkages. The decomposition of the overall effect into geometrical and electrostatic contributions evidence (i) the key role of an arginine (R24) and (ii) a weaker geometrical penalty for elongating the nonstructural Cys(1-15) linkage. The addition of a second electron leads to the formation of the dithiolate Cys(1,15), favored by more than 1 eV over other adducts (either dithiolates or diradical dianionic species). This can be traced back to a structural reorganization, with a flip of R24 side chain. Its positively charged extremity points almost equidistantly toward one thiolate -CH2-S(-), hence stabilizing this dianion.
Publisher: American Chemical Society (ACS)
Date: 02-07-2019
DOI: 10.26434/CHEMRXIV.8427116.V1
Abstract: By combining extrapolated selected configuration interaction (sCI) energies obtained with the CIPSI (Configuration Interaction using a Perturbative Selection made Iteratively) algorithm with the recently proposed short-range density-functional correction for basis-set incompleteness [Giner et al., J. Chem. Phys. 2018, 149, 194301], we show that one can get chemically accurate vertical and adiabatic excitation energies with, typically, augmented double-ζ basis sets. We illustrate the present approach on various types of excited states (valence, Rydberg, and double excitations) in several small organic molecules (methylene, water, ammonia, carbon dimer and ethylene). The present study clearly evidences that special care has to be taken with very diffuse excited states where the present correction does not catch the radial incompleteness of the one-electron basis set.
Publisher: AIP Publishing
Date: 17-07-2023
DOI: 10.1063/5.0159853
Abstract: In recent years, Green’s function methods have garnered considerable interest due to their ability to target both charged and neutral excitations. Among them, the well-established GW approximation provides accurate ionization potentials and electron affinities and can be extended to neutral excitations using the Bethe–Salpeter equation (BSE) formalism. Here, we investigate the connections between various Green’s function methods and evaluate their performance for charged and neutral excitations. Comparisons with other widely known second-order wave function methods are also reported. Additionally, we calculate the singlet-triplet gap of cycl[3,3,3]azine, a model molecular emitter for thermally activated delayed fluorescence, which has the particularity of having an inverted gap thanks to a substantial contribution from the double excitations. We demonstrate that, within the GW approximation, a second-order BSE kernel with dynamical correction is required to predict this distinctive characteristic.
Publisher: American Chemical Society (ACS)
Date: 23-07-2008
DOI: 10.1021/CT800161M
Abstract: An active site containing a Cys-X-X-Cys motif (CXXC), where X denotes any amino acid, is always found in the thiol-disulfide oxidoreductase superfamily. Because of its very high propensity for N-termini of α-helices, we examine the effect of this secondary structure on the disulfide-linked CXXC electron affinity. A Cys-Gly-Pro-Cys motif (CGPC) is chosen as an ex le, as it is the canonical motif found in thioredoxins. QM/MM calculations (MP2/6-31+G**:CHARMM) establish that the electron capture is strongly favored by an N-terminal α-helix, due to the positive electrostatic potential in the vicinity of the active site. The enhancement of adiabatic electron affinity accounts for ca. 0.9 eV for a 12-residues helix and rapidly converges as the number of alanine residues increases. A close agreement between a reference thioredoxin (Trx h) and the corresponding model peptide is found (respectively +2.20 and +2.12 eV), in parallel with experimental redox potentials [Iqbalsyah et al. Protein Sci. 2006, 15, 2026-2030]. This suggests a simple additive rule for geometrical and electrostatic effects. The electron affinity of the CXXC active site is first considered in an isolated way. Then, the strong modulation of the electrostatic field created by the α-helix can be added up. This simple partition scheme allows a proper quantification of the ease of attachment of a low-energy electron.
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C6CP06801D
Abstract: In this work we explore the nature of chemical bonding in one dimensional molecules.
Publisher: AIP Publishing
Date: 02-11-2020
DOI: 10.1063/5.0027617
Abstract: Following the recent work of Eriksen et al. [J. Phys. Chem. Lett. 11, 8922 (2020)], we report the performance of the configuration interaction using a perturbative selection made iteratively method on the non-relativistic frozen-core correlation energy of the benzene molecule in the cc-pVDZ basis. Following our usual protocol, we obtain a correlation energy of −863.4 mEh, which agrees with the theoretical estimate of −863 mEh proposed by Eriksen et al. [J. Phys. Chem. Lett. 11, 8922 (2020)] using an extensive array of highly accurate new electronic structure methods.
Publisher: American Chemical Society (ACS)
Date: 20-12-2019
DOI: 10.26434/CHEMRXIV.11347994.V1
Abstract: The search for new ab initio models rapidly delivering accurate excited state energies and properties is one of the most active research lines of theoretical chemistry. Along with these methodological developments, the performances of known methods are constantly reassessed thanks to the emergence of new benchmark values. In this Letter, we show that, in contrast to previous claims, the third-order algebraic diagrammatic construction, ADC(3), does not yield transition energies of the same quality as the third-order coupled cluster method, CC3. There is indeed a significant difference in terms of accuracy between the two approaches, as we clearly and unambiguously demonstrate here thanks to extensive comparisons with several hundreds high-quality vertical transition energies obtained with FCI, CCSDTQ, and CCSDT. Direct comparisons with experimental 0-0 energies of small- and medium-size organic molecules support the same conclusion, which holds for both valence and Rydberg transitions, as well as singlet and triplet states. In regards of these results, we introduce a composite method that we named ADC(2.5) which consists in averaging the ADC(2) and ADC(3) excitation energies. Although ADC(2.5) does not match the CC3 accuracy, it significantly improves the ADC(3) results, especially for vertical energies. We hope that the present contribution will stimulate further developments and, in particular, improvements of the ADC-type methods which have the indisputable advantage of being computationally lighter than their equivalent-order CC variants.
Publisher: AIP Publishing
Date: 11-11-2015
DOI: 10.1063/1.4935374
Abstract: The form of the wave function at three-electron coalescence points is examined for several spin states using an alternative method to the usual Fock expansion. We find that, in two- and three-dimensional systems, the non-analytical nature of the wave function is characterized by the appearance of logarithmic terms, reminiscent of those that appear as both electrons approach the nucleus of the helium atom. The explicit form of these singularities is given in terms of the interelectronic distances for a doublet and two quartet states of three electrons in a harmonic well.
Publisher: Wiley
Date: 24-06-2012
DOI: 10.1002/QUA.23155
Publisher: Springer Science and Business Media LLC
Date: 19-05-2004
Publisher: Wiley
Date: 2007
DOI: 10.1002/QUA.21410
Publisher: Informa UK Limited
Date: 08-04-2022
Publisher: Informa UK Limited
Date: 02-09-2010
Publisher: American Physical Society (APS)
Date: 30-06-2009
Publisher: AIP Publishing
Date: 28-01-2017
DOI: 10.1063/1.4974839
Abstract: Wigner crystals (WCs) are electronic phases peculiar to low-density systems, particularly in the uniform electron gas. Since its introduction in the early twentieth century, this model has remained essential to many aspects of electronic structure theory and condensed-matter physics. Although the (lowest-energy) ground-state WC (GSWC) has been thoroughly studied, the properties of excited-state WCs (ESWCs) are basically unknown. To bridge this gap, we present a well-defined procedure to obtain an entire family of ESWCs in a one-dimensional electron gas using a symmetry-broken mean-field approach. While the GSWC is a commensurate crystal (i.e., the number of density maxima equals the number of electrons), these ESWCs are incommensurate crystals exhibiting more or less maxima. Interestingly, they are lower in energy than the (uniform) Fermi fluid state. For some of these ESWCs, we have found asymmetrical band gaps, which would lead to anisotropic conductivity. These properties are associated with unusual characteristics in their electronic structure.
Publisher: AIP Publishing
Date: 08-2023
DOI: 10.1063/5.0163846
Abstract: We present an equation generator algorithm that utilizes second-quantized operators in normal order with respect to a correlated or non-correlated reference and the corresponding Wick theorem. The algorithm proposed here, written with Mathematica, enables the generation of non-redundant strings of second-quantized operators that, after classification, are directly assigned to many-body term quantities used to construct the many-body Hamiltonian. We demonstrate the capabilities of the algorithm by computing the coupled-cluster litude equations and various blocks of the equation-of-motion many-body Hamiltonian. A comprehensive description of this four-step algorithm is provided alongside concrete ex les.
Publisher: AIP Publishing
Date: 17-07-2017
DOI: 10.1063/1.4992127
Abstract: A hybrid stochastic-deterministic approach for computing the second-order perturbative contribution E(2) within multireference perturbation theory (MRPT) is presented. The idea at the heart of our hybrid scheme—based on a reformulation of E(2) as a sum of elementary contributions associated with each determinant of the MR wave function—is to split E(2) into a stochastic and a deterministic part. During the simulation, the stochastic part is gradually reduced by dynamically increasing the deterministic part until one reaches the desired accuracy. In sharp contrast with a purely stochastic Monte Carlo scheme where the error decreases indefinitely as t−1/2 (where t is the computational time), the statistical error in our hybrid algorithm displays a polynomial decay ∼t−n with n = 3–4 in the ex les considered here. If desired, the calculation can be carried on until the stochastic part entirely vanishes. In that case, the exact result is obtained with no error bar and no noticeable computational overhead compared to the fully deterministic calculation. The method is illustrated on the F2 and Cr2 molecules. Even for the largest case corresponding to the Cr2 molecule treated with the cc-pVQZ basis set, very accurate results are obtained for E(2) for an active space of (28e, 176o) and a MR wave function including up to 2×107 determinants.
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0FD90025G
Publisher: Elsevier BV
Date: 05-2012
Publisher: Springer Science and Business Media LLC
Date: 13-12-2012
Publisher: American Chemical Society (ACS)
Date: 10-05-2022
Publisher: Springer Science and Business Media LLC
Date: 15-02-2007
Publisher: Informa UK Limited
Date: 27-04-2012
Publisher: IOP Publishing
Date: 03-06-2021
Abstract: We explore the non-Hermitian extension of quantum chemistry in the complex plane and its link with perturbation theory. We observe that the physics of a quantum system is intimately connected to the position of complex-valued energy singularities, known as exceptional points. After presenting the fundamental concepts of non-Hermitian quantum chemistry in the complex plane, including the mean-field Hartree–Fock approximation and Rayleigh–Schrödinger perturbation theory, we provide a historical overview of the various research activities that have been performed on the physics of singularities. In particular, we highlight seminal work on the convergence behaviour of perturbative series obtained within Møller–Plesset perturbation theory, and its links with quantum phase transitions. We also discuss several resummation techniques (such as Padé and quadratic approximants) that can improve the overall accuracy of the Møller–Plesset perturbative series in both convergent and ergent cases. Each of these points is illustrated using the Hubbard dimer at half filling, which proves to be a versatile model for understanding the subtlety of analytically-continued perturbation theory in the complex plane.
Publisher: AIP Publishing
Date: 25-08-2015
DOI: 10.1063/1.4929353
Abstract: By combining variational Monte Carlo (VMC) and complete-basis-set limit Hartree-Fock (HF) calculations, we have obtained near-exact correlation energies for low-density same-spin electrons on a three-dimensional sphere (3-sphere), i.e., the surface of a four-dimensional ball. In the VMC calculations, we compare the efficacies of two types of one-electron basis functions for these strongly correlated systems and analyze the energy convergence with respect to the quality of the Jastrow factor. The HF calculations employ spherical Gaussian functions (SGFs) which are the curved-space analogs of Cartesian Gaussian functions. At low densities, the electrons become relatively localized into Wigner crystals, and the natural SGF centers are found by solving the Thomson problem (i.e., the minimum-energy arrangement of n point charges) on the 3-sphere for various values of n. We have found 11 special values of n whose Thomson sites are equivalent. Three of these are the vertices of four-dimensional Platonic solids — the hyper-tetrahedron (n = 5), the hyper-octahedron (n = 8), and the 24-cell (n = 24) — and a fourth is a highly symmetric structure (n = 13) which has not previously been reported. By calculating the harmonic frequencies of the electrons around their equilibrium positions, we also find the first-order vibrational corrections to the Thomson energy.
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2CP02827A
Abstract: In this paper, the history, present status, and future of density-functional theory (DFT) is informally reviewed and discussed by 70 workers in the field, including molecular scientists, materials scientists, method developers and practitioners.
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4CP03571B
Abstract: Orbital basis functions in a one-dimensional triatomic molecule ABC.
Publisher: AIP Publishing
Date: 06-2020
DOI: 10.1063/5.0007388
Abstract: We report a local, weight-dependent correlation density-functional approximation that incorporates information about both ground and excited states in the context of density functional theory for ensembles (eDFT). This density-functional approximation for ensembles is specially designed for the computation of single and double excitations within Gross–Oliveira–Kohn DFT (i.e., eDFT for neutral excitations) and can be seen as a natural extension of the ubiquitous local-density approximation in the context of ensembles. The resulting density-functional approximation, based on both finite and infinite uniform electron gas models, automatically incorporates the infamous derivative discontinuity contributions to the excitation energies through its explicit ensemble weight dependence. Its accuracy is illustrated by computing single and double excitations in one-dimensional (1D) many-electron systems in the weak, intermediate, and strong correlation regimes. Although the present weight-dependent functional has been specifically designed for 1D systems, the methodology proposed here is general, i.e., directly applicable to the construction of weight-dependent functionals for realistic three-dimensional systems, such as molecules and solids.
Publisher: AIP Publishing
Date: 22-12-2009
DOI: 10.1063/1.3275519
Abstract: We consider the high-density-limit correlation energy Ec in D≥2 dimensions for the S1 ground states of three two-electron systems: helium (in which the electrons move in a Coulombic field), spherium (in which they move on the surface of a sphere), and hookium (in which they move in a quadratic potential). We find that the Ec values are strikingly similar, depending strongly on D but only weakly on the external potential. We conjecture that for large D, the limiting correlation energy Ec∼−δ2/8 in any confining external potential, where δ=1/(D−1).
Publisher: American Chemical Society (ACS)
Date: 27-01-2020
Abstract: Following our previous work focusing on compounds containing up to 3 non-hydrogen atoms [
Publisher: AIP Publishing
Date: 04-05-2020
DOI: 10.1063/5.0002892
Abstract: We extend to strongly correlated molecular systems the recently introduced basis-set incompleteness correction based on density-functional theory (DFT) [E. Giner et al., J. Chem. Phys. 149, 194301 (2018)]. This basis-set correction relies on a mapping between wave-function calculations in a finite basis set and range-separated DFT (RSDFT) through the definition of an effective non- ergent interaction corresponding to the electron–electron Coulomb interaction projected in the finite basis set. This enables the use of RSDFT-type complementary density functionals to recover the dominant part of the short-range correlation effects missing in this finite basis set. To study both weak and strong correlation regimes, we consider the potential energy curves of the H10, N2, O2, and F2 molecules up to the dissociation limit, and we explore various approximations of complementary functionals fulfilling two key properties: spin-multiplet degeneracy (i.e., independence of the energy with respect to the spin projection Sz) and size consistency. Specifically, we investigate the dependence of the functional on different types of on-top pair densities and spin polarizations. The key result of this study is that the explicit dependence on the on-top pair density allows one to completely remove the dependence on any form of spin polarization without any significant loss of accuracy. Quantitatively, we show that the basis-set correction reaches chemical accuracy on atomization energies with triple-ζ quality basis sets for most of the systems studied here. In addition, the present basis-set incompleteness correction provides smooth potential energy curves along the whole range of internuclear distances.
Publisher: AIP Publishing
Date: 07-2022
DOI: 10.1063/5.0095887
Abstract: Based on 280 reference vertical transition energies of various excited states (singlet, triplet, valence, Rydberg, n → π*, π → π*, and double excitations) extracted from the QUEST database, we assess the accuracy of complete-active-space third-order perturbation theory (CASPT3), in the context of molecular excited states. When one applies the disputable ionization-potential-electron-affinity (IPEA) shift, we show that CASPT3 provides a similar accuracy as its second-order counterpart, CASPT2, with the same mean absolute error of 0.11 eV. However, as already reported, we also observe that the accuracy of CASPT3 is almost insensitive to the IPEA shift, irrespective of the transition type and system size, with a small reduction in the mean absolute error to 0.09 eV when the IPEA shift is switched off.
Publisher: AIP Publishing
Date: 21-03-2017
DOI: 10.1063/1.4978409
Abstract: We show how one can construct a simple exchange functional by extending the well-know local-density approximation (LDA) to finite uniform electron gases. This new generalized local-density approximation functional uses only two quantities: the electron density ρ and the curvature of the Fermi hole α. This alternative “rung 2” functional can be easily coupled with generalized-gradient approximation (GGA) functionals to form a new family of “rung 3” meta-GGA (MGGA) functionals that we have named factorizable MGGAs. Comparisons are made with various LDA, GGA, and MGGA functionals for atoms and molecules.
Publisher: American Chemical Society (ACS)
Date: 24-04-2019
DOI: 10.26434/CHEMRXIV.7749485.V3
Abstract: Quantum Package is an open-source programming environment for quantum chemistry specially designed for wave function methods. Its main goal is the development of determinant-driven selected configuration interaction (sCI) methods and multi-reference second-order perturbation theory (PT2). The determinant-driven framework allows the programmer to include any arbitrary set of determinants in the reference space, hence providing greater method- ological freedoms. The sCI method implemented in Quantum Package is based on the CIPSI (Configuration Interaction using a Perturbative Selection made Iteratively) algorithm which complements the variational sCI energy with a PT2 correction. Additional external plugins have been recently added to perform calculations with multireference coupled cluster theory and range-separated density-functional theory. All the programs are developed with the IRPF90 code generator, which simplifies collaborative work and the development of new features. Quantum Package strives to allow easy implementation and experimentation of new methods, while making parallel computation as simple and efficient as possible on modern supercomputer architectures. Currently, the code enables, routinely, to realize runs on roughly 2 000 CPU cores, with tens of millions of determinants in the reference space. Moreover, we have been able to push up to 12 288 cores in order to test its parallel efficiency. In the present manuscript, we also introduce some key new developments: i) a renormalized second-order perturbative correction for efficient extrapolation to the full CI limit, and ii) a stochastic version of the CIPSI selection performed simultaneously to the PT2 calculation at no extra cost.
Publisher: Elsevier
Date: 2021
Publisher: Elsevier BV
Date: 09-2010
DOI: 10.1016/J.JINORGBIO.2010.04.002
Abstract: The structural and spectroscopic properties of [Ru(phen)(2)(dppz)](2+) and [Ru(tap)(2)(dppz)](2+) (phen=1,10-phenanthroline tap=1,4,5,8-tetraazaphenanthrene dppz=dipyridophenazine ) have been investigated by means of density functional theory (DFT), time-dependent DFT (TD-DFT) within the polarized continuum model (IEF-PCM) and quantum mechanics/molecular mechanics (QM/MM) calculations. The model of the Delta and Lambda enantiomers of Ru(II) intercalated in DNA in the minor and major grooves is limited to the metal complexes intercalated in two guanine-cytosine base pairs. The main experimental spectral features of these complexes reported in DNA or synthetic polynucleotides are better reproduced by the theoretical absorption spectra of the Delta enantiomers regardless of intercalation mode (major or minor groove). This is especially true for [Ru(phen)(2)(dppz)](2+). The visible absorption of [Ru(tap)(2)(dppz)](2+) is governed by the MLCT(tap) transitions regardless of the environment (water, acetonitrile or bases pair), the visible absorption of [Ru(phen)(2)(dppz)](2+) is characterized by transitions to metal-to-ligand-charge-transfer MLCT(dppz) in water and acetonitrile and to MLCT(phen) when intercalated in DNA. The response of the IL(dppz) state to the environment is very sensitive. In vacuum, water and acetonitrile these transitions are characterized by significant oscillator strengths and their positions depend significantly on the medium with blue shifts of about 80 nm when going from vacuum to solvent. When the complex is intercalated in the guanine-cytosine base pairs the (1)IL(dppz) transition contributes mainly to the band at 370 nm observed in the spectrum of [Ru(phen)(2)(dppz)](2+) and to the band at 362 nm observed in the spectrum of [Ru(tap)(2)(dppz)](2+).
Publisher: American Chemical Society (ACS)
Date: 25-04-2019
DOI: 10.26434/CHEMRXIV.8038541.V1
Abstract: We report a universal density-based basis-set incom- pleteness correction that can be applied to any wave function method. The present correction, which ap- propriately vanishes in the complete basis set (CBS) limit, relies on short-range correlation density func- tionals (with multi-determinant reference) from range- separated density-functional theory (RS-DFT) to esti- mate the basis-set incompleteness error. Contrary to conventional RS-DFT schemes which require an ad hoc range-separation parameter μ, the key ingredient here is a range-separation function μ(r) that automatically adapts to the spatial non-homogeneity of the basis-set incompleteness error. As illustrative ex les, we show how this density-based correction allows us to obtain CCSD(T) atomization and correlation energies near the CBS limit for the G2 set of molecules with compact Gaussian basis sets.
Publisher: American Chemical Society (ACS)
Date: 12-2020
Publisher: AIP Publishing
Date: 15-12-2022
DOI: 10.1063/5.0130837
Abstract: Here, we build on the works of Scuseria et al. [J. Chem. Phys. 129, 231101 (2008)] and Berkelbach [J. Chem. Phys. 149, 041103 (2018)] to show connections between the Bethe–Salpeter equation (BSE) formalism combined with the GW approximation from many-body perturbation theory and coupled-cluster (CC) theory at the ground- and excited-state levels. In particular, we show how to recast the GW and Bethe–Salpeter equations as non-linear CC-like equations. Similitudes between BSE@GW and the similarity-transformed equation-of-motion CC method are also put forward. The present work allows us to easily transfer key developments and the general knowledge gathered in CC theory to many-body perturbation theory. In particular, it may provide a path for the computation of ground- and excited-state properties (such as nuclear gradients) within the GW and BSE frameworks.
Publisher: AIP Publishing
Date: 10-2021
DOI: 10.1063/5.0065314
Abstract: Following our recent work on the benzene molecule [P.-F. Loos, Y. Damour, and A. Scemama, J. Chem. Phys. 153, 176101 (2020)], motivated by the blind challenge of Eriksen et al. [J. Phys. Chem. Lett. 11, 8922 (2020)] on the same system, we report accurate full configuration interaction (FCI) frozen-core correlation energy estimates for 12 five- and six-membered ring molecules (cyclopentadiene, furan, imidazole, pyrrole, thiophene, benzene, pyrazine, pyridazine, pyridine, pyrimidine, s-tetrazine, and s-triazine) in the standard correlation-consistent double-ζ Dunning basis set (cc-pVDZ). Our FCI correlation energy estimates, with an estimated error smaller than 1 millihartree, are based on energetically optimized-orbital selected configuration interaction calculations performed with the configuration interaction using a perturbative selection made iteratively algorithm. Having at our disposal these accurate reference energies, the respective performance and convergence properties of several popular and widely used families of single-reference quantum chemistry methods are investigated. In particular, we study the convergence properties of (i) the Møller–Plesset perturbation series up to fifth-order (MP2, MP3, MP4, and MP5), (ii) the iterative approximate coupled-cluster series CC2, CC3, and CC4, and (iii) the coupled-cluster series CCSD, CCSDT, and CCSDTQ. The performance of the ground-state gold standard CCSD(T) as well as the completely renormalized CC model, CR-CC(2,3), is also investigated. We show that MP4 provides an interesting accuracy/cost ratio, while MP5 systematically worsens the correlation energy estimates. In addition, CC3 outperforms CCSD(T) and CR-CC(2,3), as well as its more expensive parent CCSDT. A similar trend is observed for the methods including quadruple excitations, where the CC4 model is shown to be slightly more accurate than CCSDTQ, both methods providing correlation energies within 2 millihartree of the FCI limit.
Publisher: American Physical Society (APS)
Date: 08-06-2016
Publisher: American Chemical Society (ACS)
Date: 07-10-2008
DOI: 10.1021/JP806465E
Abstract: Integrated molecular orbital-molecular orbital (IMOMO) calculations on 17 short disulfide-bridged peptides (up to 16 residues, with at most five intraloop residues) were performed to elucidate some factors controlling their electron capture. These illustrative systems display contrasted behaviors, shedding light on several criteria of differentiation: size, shape, and rigidity of the disulfide-linking loop, intramolecular hydrogen bonds, etc. The geometrical malleability of disulfide radical anions, whose existence and role as intermediate have been evidenced, is discussed. The disulfide elongation (by ca. 0.7 A) upon electron capture induces "soft" structural damages for these turn structures, with a weakening or cleavage of vicinal hydrogen bond(s). On the basis of a series of six Cys-Alan-Cys peptides, it is proposed that electron affinity reflects the topological frustration of these short and highly constrained structures. Results for a series of amino acid mutations are analyzed for the Cys-Xxx-Yyy-Cys motif, common to redox enzymes of the thioredoxin superfamily.
Publisher: Elsevier BV
Date: 06-2008
Publisher: American Chemical Society (ACS)
Date: 03-03-2020
Publisher: AIP Publishing
Date: 03-08-2021
DOI: 10.1063/5.0056968
Abstract: Fractional-spin errors are inherent in all current approximate density functionals, including Hartree–Fock theory, and their origin has been related to strong static correlation effects. The conventional way to encode fractional-spin calculations is to construct an ensemble density that scales between the high-spin and low-spin densities. In this article, we explore the variation of the Hartree–Fock fractional-spin (or ghost-interaction) error in one-electron systems using restricted and unrestricted ensemble densities and the exact generalized Hartree–Fock representation. By considering the hydrogen atom and H+2 cation, we analyze how the unrestricted and generalized Hartree–Fock schemes minimize this error by localizing the electrons or rotating the spin coordinates. We also reveal a clear similarity between the Coulomb hole of He-like ions and the density depletion near the nucleus induced by the fractional-spin error in the unpolarized hydrogen atom. Finally, we analyze the effect of the fractional-spin error on the Møller–Plesset adiabatic connection, excited states, and functional- and density-driven errors.
Publisher: Wiley
Date: 17-02-2021
DOI: 10.1002/WCMS.1517
Abstract: We describe our efforts of the past few years to create a large set of more than 500 highly accurate vertical excitation energies of various natures ( π → π * , n → π * , double excitation, Rydberg, singlet, doublet, triplet, etc.) in small‐ and medium‐sized molecules. These values have been obtained using an incremental strategy which consists in combining high‐order coupled cluster and selected configuration interaction calculations using increasingly large diffuse basis sets in order to reach high accuracy. One of the key aspects of the so‐called QUEST database of vertical excitations is that it does not rely on any experimental values, avoiding potential biases inherently linked to experiments and facilitating theoretical cross comparisons. Following this composite protocol, we have been able to produce theoretical best estimates (TBEs) with the aug‐cc‐pVTZ basis set for each of these transitions, as well as basis set corrected TBEs (i.e., near the complete basis set limit) for some of them. The TBEs/aug‐cc‐pVTZ have been employed to benchmark a large number of (lower‐order) wave function methods such as CIS(D), ADC(2), CC2, STEOM‐CCSD, CCSD, CCSDR(3), CCSDT‐3, ADC(3), CC3, NEVPT2, and so on (including spin‐scaled variants). In order to gather the huge amount of data produced during the QUEST project, we have created a website ( lcpq.github.io/QUESTDB_website ) where one can easily test and compare the accuracy of a given method with respect to various variables such as the molecule size or its family, the nature of the excited states, the type of basis set, and so on. We hope that the present review will provide a useful summary of our effort so far and foster new developments around excited‐state methods. This article is categorized under: Electronic Structure Theory Ab Initio Electronic Structure Methods
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0FD00059K
Abstract: We discuss the construction of first-rung weight-dependent exchange–correlation density-functional approximations for He and H 2 specifically designed for the computation of double excitations within Gross–Oliveira–Kohn-DFT.
Publisher: American Chemical Society (ACS)
Date: 31-12-2019
Abstract: Similar to other electron correlation methods, many-body perturbation theory methods based on Green's functions, such as the so-called
Publisher: AIP Publishing
Date: 14-10-2019
DOI: 10.1063/1.5122976
Abstract: By combining extrapolated selected configuration interaction (sCI) energies obtained with the Configuration Interaction using a Perturbative Selection made Iteratively algorithm with the recently proposed short-range density-functional correction for basis-set incompleteness [E. Giner et al., J. Chem. Phys. 149, 194301 (2018)], we show that one can get chemically accurate vertical and adiabatic excitation energies with, typically, augmented double-ζ basis sets. We illustrate the present approach on various types of excited states (valence, Rydberg, and double excitations) in several small organic molecules (methylene, water, ammonia, carbon dimer, and ethylene). The present study clearly evidences that special care has to be taken with very diffuse excited states where the present correction does not catch the radial incompleteness of the one-electron basis set.
Publisher: AIP Publishing
Date: 17-03-2014
DOI: 10.1063/1.4867910
Abstract: We introduce a generalization (gLDA) of the traditional Local Density Approximation (LDA) within density functional theory. The gLDA uses both the one-electron Seitz radius rs and a two-electron hole curvature parameter η at each point in space. The gLDA reduces to the LDA when applied to the infinite homogeneous electron gas but, unlike the LDA, it is also exact for finite uniform electron gases on spheres. We present an explicit gLDA functional for the correlation energy of electrons that are confined to a one-dimensional space and compare its accuracy with LDA, second- and third-order Møller-Plesset perturbation energies, and exact calculations for a variety of inhomogeneous systems.
Publisher: AIP Publishing
Date: 11-06-2021
DOI: 10.1063/5.0055994
Abstract: We report the first investigation of the performance of EOM-CC4—an approximate equation-of-motion coupled-cluster model, which includes iterative quadruple excitations—for vertical excitation energies in molecular systems. By considering a set of 28 excited states in 10 small molecules for which we have computed CC with singles, doubles, triples, quadruples, and pentuples and full configuration interaction reference energies, we show that, in the case of excited states with a dominant contribution from the single excitations, CC4 yields excitation energies with sub-kJ mol−1 accuracy (i.e., error below 0.01 eV), in very close agreement with its more expensive CC with singles, doubles, triples, and quadruples parent. Therefore, if one aims at high accuracy, CC4 stands as a highly competitive approximate method to model molecular excited states, with a significant improvement over both CC3 and CC with singles, doubles, and triples. Our results also evidence that, although the same qualitative conclusions hold, one cannot reach the same level of accuracy for transitions with a dominant contribution from the double excitations.
Publisher: AIP Publishing
Date: 11-07-2017
DOI: 10.1063/1.4991733
Abstract: We report the three main ingredients to calculate three- and four-electron integrals over Gaussian basis functions involving Gaussian geminal operators: fundamental integrals, upper bounds, and recurrence relations. In particular, we consider the three- and four-electron integrals that may arise in explicitly correlated F12 methods. A straightforward method to obtain the fundamental integrals is given. We derive vertical, transfer, and horizontal recurrence relations to build up angular momentum over the centers. Strong, simple, and scaling-consistent upper bounds are also reported. This latest ingredient allows us to compute only the O(N2) significant three- and four-electron integrals, avoiding the computation of the very large number of negligible integrals.
Publisher: Elsevier BV
Date: 2014
Publisher: AIP Publishing
Date: 02-01-2020
DOI: 10.1063/1.5140669
Abstract: The ΔNO method for static correlation is combined with second-order Møller-Plesset perturbation theory (MP2) and coupled-cluster singles and doubles (CCSD) to account for dynamic correlation. The MP2 and CCSD expressions are adapted from finite-temperature CCSD, which includes orbital occupancies and vacancies, and expanded orbital summations. Correlation is partitioned with the aid of d ing factors incorporated into the MP2 and CCSD residual equations. Potential energy curves for a selection of diatomics are in good agreement with extrapolated full configuration interaction results and on par with conventional multireference approaches.
Publisher: American Chemical Society (ACS)
Date: 30-03-2016
Abstract: Explicitly correlated F12 methods are becoming the first choice for high-accuracy molecular orbital calculations and can often achieve chemical accuracy with relatively small Gaussian basis sets. In most calculations, the many three- and four-electron integrals that formally appear in the theory are avoided through judicious use of resolutions of the identity (RI). However, for the intrinsic accuracy of the F12 wave function to not be jeopardized, the associated RI auxiliary basis set must be large. Here, inspired by the Head-Gordon-Pople and PRISM algorithms for two-electron integrals, we present an algorithm to directly compute three-electron integrals over Gaussian basis functions and a very general class of three-electron operators without invoking RI approximations. A general methodology to derive vertical, transfer, and horizontal recurrence relations is also presented.
Publisher: American Physical Society (APS)
Date: 18-09-2009
Publisher: American Physical Society (APS)
Date: 07-09-2010
Publisher: American Chemical Society (ACS)
Date: 26-07-2021
Publisher: American Chemical Society (ACS)
Date: 06-05-2021
Publisher: Wiley
Date: 2007
DOI: 10.1002/QUA.21182
Publisher: American Chemical Society (ACS)
Date: 25-01-2021
Publisher: American Chemical Society (ACS)
Date: 10-05-2018
Abstract: We report an exhaustive study of the performance of different variants of Green function methods for the spherium model in which two electrons are confined to the surface of a sphere and interact via a genuine long-range Coulomb operator. We show that the spherium model provides a unique paradigm to study electronic correlation effects from the weakly correlated regime to the strongly correlated regime, since the mathematics are simple while the physics is rich. We compare perturbative GW, partially self-consistent GW and second-order Green function (GF2) methods for the computation of ionization potentials, electron affinities, energy gaps, correlation energies as well as singlet and triplet neutral excitations by solving the Bethe-Salpeter equation (BSE). We discuss the problem of self-screening in GW and show that it can be partially solved with a second-order screened exchange correction (SOSEX). We find that, in general, self-consistency deteriorates the results with respect to those obtained within perturbative approaches with a Hartree-Fock starting point. Finally, we unveil an important problem of partial self-consistency in GW: in the weakly correlated regime, it can produce artificial discontinuities in the self-energy caused by satellite resonances with large weights.
Publisher: Elsevier BV
Date: 06-2009
Publisher: American Chemical Society (ACS)
Date: 07-08-2020
Publisher: Elsevier
Date: 2019
Publisher: American Chemical Society (ACS)
Date: 11-12-2020
Publisher: American Chemical Society (ACS)
Date: 25-02-2019
Abstract: Using a series of increasingly refined wave function methods able to tackle electronic excited states, namely ADC(2), CC2, CCSD, CCSDR(3), and CC3, we investigate the interplay between geometries and 0-0 energies. We show that, due to a strong and nearly systematic error cancelation between the vertical transition and geometrical reorganization energies, CC2 and CCSD structures can be used to obtain chemically accurate 0-0 energies, though the underlying geometries are rather far from the reference ones and would deliver significant errors for several chemical and physical properties. This indicates that obtaining 0-0 energies matching experiment does not demonstrate the quality of the underlying geometrical parameters. By computing CC3 total energies on CCSD structures, we model a large set of compounds (including radicals) and electronic transitions (including singlet-triplet excitations) and successfully reach chemical accuracy in a near systematic way. Indeed, for this particular set, we obtain a mean absolute error as small as 0.032 eV, chemical accuracy (error smaller than 1 kcal·mol
Publisher: American Chemical Society (ACS)
Date: 31-07-2018
DOI: 10.1021/ACS.JPCLETT.8B02058
Abstract: Ab initio calculation of electronic excitation energies with chemical accuracy (ca. 1 kcal·mol
Publisher: AIP Publishing
Date: 03-11-2020
DOI: 10.1063/5.0026324
Abstract: By combining density-functional theory (DFT) and wave function theory via the range separation (RS) of the interelectronic Coulomb operator, we obtain accurate fixed-node diffusion Monte Carlo (FN-DMC) energies with compact multi-determinant trial wave functions. In particular, we combine here short-range exchange-correlation functionals with a flavor of selected configuration interaction known as configuration interaction using a perturbative selection made iteratively (CIPSI), a scheme that we label RS-DFT-CIPSI. One of the take-home messages of the present study is that RS-DFT-CIPSI trial wave functions yield lower fixed-node energies with more compact multi-determinant expansions than CIPSI, especially for small basis sets. Indeed, as the CIPSI component of RS-DFT-CIPSI is relieved from describing the short-range part of the correlation hole around the electron–electron coalescence points, the number of determinants in the trial wave function required to reach a given accuracy is significantly reduced as compared to a conventional CIPSI calculation. Importantly, by performing various numerical experiments, we evidence that the RS-DFT scheme essentially plays the role of a simple Jastrow factor by mimicking short-range correlation effects, hence avoiding the burden of performing a stochastic optimization. Considering the 55 atomization energies of the Gaussian-1 benchmark set of molecules, we show that using a fixed value of μ = 0.5 bohr−1 provides effective error cancellations as well as compact trial wave functions, making the present method a good candidate for the accurate description of large chemical systems.
Publisher: Springer Science and Business Media LLC
Date: 02-05-2017
DOI: 10.1007/S00894-017-3347-3
Abstract: We propose a new self-consistent field (SCF) algorithm based on an iterative, partially stochastic "Divide & Conquer"-type approach. This new SCF algorithm is a simple variant of the usual SCF procedure and can be easily implemented in parallel. A detailed description of the algorithm is reported. We illustrate this new method on one-dimensional hydrogen chains and three-dimensional hydrogen clusters. Graphical Abstract Stochastic partition of the molecular orbitals.
Publisher: AIP Publishing
Date: 17-06-2010
DOI: 10.1063/1.3455706
Abstract: We study the ground-state correlation energy Ec of two electrons of opposite spin confined within a D-dimensional ball (D≥2) of radius R. In the high-density regime, we report accurate results for the exact and restricted Hartree–Fock energy, using a Hylleraas-type expansion for the former and a simple polynomial basis set for the latter. By investigating the exact limiting correlation energy Ec(0)=limR→0Ec for various values of D, we test our recent conjecture [P.-F. Loos and P. M. W. Gill, J. Chem. Phys. 131, 241101 (2009)] that in the large-D limit, Ec(0)∼−δ2/8 for any spherically symmetric confining external potential, where δ=1/(D−1).
Publisher: AIP Publishing
Date: 07-12-2011
DOI: 10.1063/1.3665393
Abstract: We discuss alternative homogeneous electron gas systems in which a finite number n of electrons are confined to a D-dimensional sphere. We derive the first few terms of the high-density (rs → 0, where rs is the Seitz radius) energy expansions for these systems and show that, in the thermodynamic limit (n → ∞), these terms become identical to those of D-dimensional jellium.
Publisher: American Chemical Society (ACS)
Date: 06-04-2023
Publisher: American Physical Society (APS)
Date: 10-03-2010
Publisher: American Chemical Society (ACS)
Date: 19-12-2019
DOI: 10.26434/CHEMRXIV.11328128.V1
Abstract: Following our previous work focussing on compounds containing up to 3 non-hydrogen atoms [J. Chem. Theory Comput. 14 (2018) 4360–4379], we present here highly-accurate vertical transition energies obtained for 27 molecules encompassing 4, 5, and 6 non-hydrogen atoms: acetone, acrolein, benzene, butadiene, cyanoacetylene, cyanoformaldehyde, cyanogen, cyclopentadiene, cyclopropenone, cyclopropenethione, diacetylene, furan, glyoxal, imidazole, isobutene, methylenecyclopropene, propynal, pyrazine, pyridazine, pyridine, pyrimidine, pyrrole, tetrazine, thioacetone, thiophene, thiopropynal, and triazine. To obtain these energies, we use equation-of-motion coupled cluster theory up to the highest technically possible excitation order for these systems (CC3, EOM-CCSDT, and EOM-CCSDTQ), selected configuration interaction (SCI) calculations (with tens of millions of determinants in the reference space), as well as the multiconfigurational 𝑛-electron valence state perturbation theory (NEVPT2) method. All these approaches are applied in combination with diffuse-containing atomic basis sets. For all transitions, we report at least CC3/aug-cc-pVQZ vertical excitation energies as well as CC3/aug-cc-pVTZ oscillator strengths for each dipole-allowed transition. We show that CC3 almost systematically delivers transition energies in agreement with higher-level methods with a typical deviation of ±0.04 eV, except for transitions with a dominant double excitation character where the error is much larger. The present contribution gathers a large, erse and accurate set of more than 200 highly-accurate transition energies for states of various natures (valence, Rydberg, singlet, triplet, 𝑛 → 𝜋★, 𝜋 → 𝜋★, . . . ). We use this series of theoretical best estimates to benchmark a series of popular methods for excited state calculations: CIS(D), ADC(2), CC2, STEOM-CCSD, EOM-CCSD, CCSDR(3), CCSDT-3, CC3, as well as NEVPT2. The results of these benchmarks are compared to the available literature data.
Publisher: SAGE Publications
Date: 2010
DOI: 10.3141/2196-05
Abstract: Traffic simulation models are frequently used to support decisions when an evacuation is planned. These models typically focus on traffic dynamics and the effect of traffic control measures to locate possible bottlenecks and predict evacuation times. However, a clear view of the crucial factors that determine evacuation time and emergent traffic states is lacking. In this paper, a structured and comprehensive sensitivity analysis identifies and quantifies the impact of variations in travel demand and network supply in the case of evacuation. The sensitivity analysis involves applying the macroscopic evacuation traffic simulation model EVAQ, in which aspects such as trip generation, departure rates, route flow rates, road capacities, and maximum speeds are systematically varied. That is accomplished using a case study that describes evacuation of the Rotterdam, Netherlands, metropolitan area. Departure rates and route flow rates are found to have a substantial nonlinear impact on network conditions and arrival pattern, particularly when the network load is relatively high, whereas trip generation and road capacities have a smaller quasilinear impact. Maximum speeds, independent of the effect on road capacities, have no significant impact on evacuation. The results, discussion, and conclusions presented can be used to identify the most important factors in (a) verifying, calibrating, and validating an evacuation model (b) designing a network for evacuation studies and (c) evaluating and testing the robustness of evacuation plans.
Publisher: Informa UK Limited
Date: 04-07-2017
DOI: 10.1080/87565641.2017.1353995
Abstract: Detailed analysis of expression judgments in Williams syndrome reveals that successful emotion categorization need not reflect "classic" information processing strategies. These in iduals draw upon a distinct set of featural details to identify happy and fearful faces that differ from those used by typically developing comparison groups: children and adults. The diagnostic visual information is also notably less interlinked in Williams syndrome, consistent with reports of diminished processing of configural information during face identity judgments. These results prompt reconsideration of typical models of face expertise by revealing that an age-appropriate profile of expression performance can be achieved via alternative routes.
Publisher: AIP Publishing
Date: 11-11-2020
DOI: 10.1063/5.0021036
Abstract: While Diffusion Monte Carlo (DMC) is in principle an exact stochastic method for ab initio electronic structure calculations, in practice, the fermionic sign problem necessitates the use of the fixed-node approximation and trial wavefunctions with approximate nodes (or zeros). This approximation introduces a variational error in the energy that potentially can be tested and systematically improved. Here, we present a computational method that produces trial wavefunctions with systematically improvable nodes for DMC calculations of periodic solids. These trial wavefunctions are efficiently generated with the configuration interaction using a perturbative selection made iteratively (CIPSI) method. A simple protocol in which both exact and approximate results for finite supercells are used to extrapolate to the thermodynamic limit is introduced. This approach is illustrated in the case of the carbon diamond using Slater–Jastrow trial wavefunctions including up to one million Slater determinants. Fixed-node DMC energies obtained with such large expansions are much improved, and the fixed-node error is found to decrease monotonically and smoothly as a function of the number of determinants in the trial wavefunction, a property opening the way to a better control of this error. The cohesive energy extrapolated to the thermodynamic limit is in close agreement with the estimated experimental value. Interestingly, this is also the case at the single-determinant level, thus, indicating a very good error cancellation in carbon diamond between the bulk and atomic total fixed-node energies when using single-determinant nodes.
Publisher: AIP Publishing
Date: 05-06-2015
DOI: 10.1063/1.4922159
Abstract: The aim of this paper is to shed light on the topology and properties of the nodes (i.e., the zeros of the wave function) in electronic systems. Using the “electrons on a sphere” model, we study the nodes of two-, three-, and four-electron systems in various ferromagnetic configurations (sp, p2, sd, pd, p3, sp2, and sp3). In some particular cases (sp, p2, sd, pd, and p3), we rigorously prove that the non-interacting wave function has the same nodes as the exact (yet unknown) wave function. The number of atomic and molecular systems for which the exact nodes are known analytically is very limited and we show here that this peculiar feature can be attributed to interdimensional degeneracies. Although we have not been able to prove it rigorously, we conjecture that the nodes of the non-interacting wave function for the sp3 configuration are exact.
Publisher: American Chemical Society (ACS)
Date: 16-03-2021
Publisher: American Chemical Society (ACS)
Date: 13-06-2023
Publisher: AIP Publishing
Date: 21-09-2020
DOI: 10.1063/5.0023168
Abstract: The Bethe–Salpeter equation (BSE) formalism is a computationally affordable method for the calculation of accurate optical excitation energies in molecular systems. Similar to the ubiquitous adiabatic approximation of time-dependent density-functional theory, the static approximation, which substitutes a dynamical (i.e., frequency-dependent) kernel by its static limit, is usually enforced in most implementations of the BSE formalism. Here, going beyond the static approximation, we compute the dynamical correction of the electron–hole screening for molecular excitation energies, thanks to a renormalized first-order perturbative correction to the static BSE excitation energies. The present dynamical correction goes beyond the plasmon-pole approximation as the dynamical screening of the Coulomb interaction is computed exactly within the random-phase approximation. Our calculations are benchmarked against high-level (coupled-cluster) calculations, allowing one to assess the clear improvement brought by the dynamical correction for both singlet and triplet optical transitions.
Publisher: American Chemical Society (ACS)
Date: 02-07-2018
Abstract: Striving to define very accurate vertical transition energies, we perform both high-level coupled cluster (CC) calculations (up to CCSDTQP) and selected configuration interaction (sCI) calculations (up to several millions of determinants) for 18 small compounds (water, hydrogen sulfide, ammonia, hydrogen chloride, dinitrogen, carbon monoxide, acetylene, ethylene, formaldehyde, methanimine, thioformaldehyde, acetaldehyde, cyclopropene, diazomethane, formamide, ketene, nitrosomethane, and the smallest streptocyanine). By systematically increasing the order of the CC expansion, the number of determinants in the CI expansion as well as the size of the one-electron basis set, we have been able to reach near full CI (FCI) quality transition energies. These calculations are carried out on CC3/ aug-cc-pVTZ geometries, using a series of increasingly large atomic basis sets systematically including diffuse functions. In this way, we define a list of 110 transition energies for states of various characters (valence, Rydberg, n → π
Publisher: American Chemical Society (ACS)
Date: 23-08-0007
Abstract: Cyclobutadiene is a well-known playground for theoretical chemists and is particularly suitable to test ground- and excited-state methods. Indeed, due to its high spatial symmetry, especially at the
Start Date: 2020
End Date: 2025
Funder: European Research Council
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