ORCID Profile
0000-0002-6779-7304
Current Organisations
Università di Padova
,
Chinese Academy of Agricultural Sciences Institute of Agricultural Resources and Regional Planning
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Quantum Chemistry | F-Block Chemistry | Inorganic Chemistry | Theoretical and Computational Chemistry | Electronic and Magnetic Properties of Condensed Matter; Superconductivity | Physical Chemistry of Materials | Condensed Matter Physics | Transition Metal Chemistry | Structural Chemistry and Spectroscopy | Atomic and Molecular Physics
ANZSRC Socio-Economic Objective (SEO)
Expanding Knowledge in the Chemical Sciences | Expanding Knowledge in the Physical Sciences | Expanding Knowledge in Technology |
Related Links
Publications
Toroidal magnetic states in molecular wheels: Interplay between isotropic exchange interactions and local magnetic anisotropy
Publisher: American Physical Society (APS)
Date: 19-06-2008
Ring-current aromaticity in open-shell systems
Publisher: Elsevier BV
Date: 2008
Molecular spintronics using noncollinear magnetic molecules
Publisher: American Physical Society (APS)
Date: 21-04-2010
Nonperturbative ab initio calculations in strong magnetic fields using London orbitals
Publisher: AIP Publishing
Date: 21-10-2008
DOI: 10.1063/1.2996525
Abstract: A self-consistent field (SCF) London-orbital computational scheme to perform gauge-origin independent nonperturbative calculations for molecules in strong magnetic fields is presented. The crucial difference in the proposed approach with respect to common-origin finite-field SCF implementations consists in the evaluation of molecular integrals over the field-dependent molecular basis functions, which is tantamount to computing molecular integrals in a hybrid Gaussian and plane-wave basis set. The implementation of a McMurchie–Davidson scheme for the calculation of the molecular integrals over London orbitals is discussed, and preliminary applications of the newly developed code to the calculation of fourth-rank hypermagnetizabilities for a set of small molecules, benzene, and cyclobutadiene are presented. The nonperturbative approach is particularly useful for studying the highly nonlinear response of paramagnetic closed-shell systems such as boron monohydride, or the π-electron response of cyclobutadiene.
An electrostatic model for the determination of magnetic anisotropy in dysprosium complexes
Publisher: Springer Science and Business Media LLC
Date: 07-10-2013
DOI: 10.1038/NCOMMS3551
Abstract: Understanding the anisotropic electronic structure of lanthanide complexes is important in areas as erse as magnetic resonance imaging, luminescent cell labelling and quantum computing. Here we present an intuitive strategy based on a simple electrostatic method, capable of predicting the magnetic anisotropy of dysprosium(III) complexes, even in low symmetry. The strategy relies only on knowing the X-ray structure of the complex and the well-established observation that, in the absence of high symmetry, the ground state of dysprosium(III) is a doublet quantized along the anisotropy axis with an angular momentum quantum number mJ=±(15)/2. The magnetic anisotropy axis of 14 low-symmetry monometallic dysprosium(III) complexes computed via high-level ab initio calculations are very well reproduced by our electrostatic model. Furthermore, we show that the magnetic anisotropy is equally well predicted in a selection of low-symmetry polymetallic complexes.
Electric-field perturbations of ring currents in π systems
Publisher: Elsevier BV
Date: 03-2005
Efficient mapping of ring currents in fullerenes and other curved carbon networks
Publisher: Elsevier BV
Date: 07-2006
Direct observation of magnetoelastic coupling in a molecular spin qubit: new insights from crystal field neutron scattering data
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D2SC05797B
Abstract: Magnetoelastic coupling has been investigated using inelastic neutron scattering. This has allowed the spin–phonon coupling of the candidate qubit Na 9 [Ho(W 5 O 18 ) 2 ]·35D 2 O to be determined in the absence of an applied magnetic field.
Why Downfield Proton Chemical Shifts Are Not Reliable Aromaticity Indicators
Publisher: American Chemical Society (ACS)
Date: 13-07-2005
DOI: 10.1021/OL051103V
Abstract: Traces of magnetizability, traces of magnetic shielding at the hydrogen nuclei, and nucleus-independent chemical shift are not reliable aromaticity quantifiers for planar conjugated hydrocarbons. A measure of aromaticity is provided by the out-of-plane tensor components, whose magnitude is influenced by the pi-ring currents. The failure of nucleus-independent chemical shift in this regard was proved for the molecule shown in the abstract graphic, sustaining a diatropic pi-current. The validity of the ring-current model is reaffirmed. [structure: see text]
Magnetic response of dithiin molecules: is there anti-aromaticity in nature?
Publisher: Elsevier BV
Date: 07-2003
Frontier-orbital ring currents and the annulene analogy
Publisher: Informa UK Limited
Date: 2004
Design and synthesis of multi-component 18π annulenic fluorofullerene ensembles suitable for donor–acceptor applications
Publisher: Royal Society of Chemistry (RSC)
Date: 2004
DOI: 10.1039/B309959H
Abstract: A series of trannulene (all-trans annulene) derivatives of [60]fullerene have been prepared by reacting C(60)F(18) with methanetricarboxylate esters that incorporate a range of photoactive functions. All the compounds have the intense emerald-green colour of fullerene trannulenes, characterised by strong bands at ca. 612 and 667 nm. Single crystal X-ray studies show that the packing varies with the nature of the addend, attributable to differing steric effects. UV/vis absorption spectra display transitions of the respective fullerene and addend models, indicating absence of electronic interactions between them in the ground state. These now provide an extensive series for testing photoactive (light-harvesting) properties, with the exceptional properties of having strong visible light absorption. Their exceptional stability is attributed to the 18[small pi] aromatic circuit, inability to undergo nucleophilic substitution without disrupting this circuit, and a curved cage region that is shielded to reagents by the three bulky addends.
Effect of the Metal Environment on the Ferromagnetic Interaction in the Co−NC−W Pairs of Octacyanotungstate(V)−Cobalt(II) Three-Dimensional Networks
Publisher: American Chemical Society (ACS)
Date: 10-03-2007
DOI: 10.1021/IC062345+
Abstract: State of the art CASSCF and CASPT2 calculations have been performed to elucidate the nature of ferromagnetism of CoII-NC-WV pairs in the three-dimensional compound [[WV(CN)2]2[(micro-CN)4CoII(H2O)2]3.4H2O]n, which has been recently synthesized and investigated by a number of experimental techniques (Herrera, J. M. Bleuzen, A. Dromzée, Y. Julve, M. Lloret, F. Verdaguer, M. Inorg. Chem. 2003, 42, 7052-7059). In this network, the Co ions are in the high-spin (S = 3/2) state, while the single unpaired electron on the W centers occupies the lowest orbital of the dz2 type of the 5d shell. In agreement with the suggestion made by Herrera et al., we find that the ferromagnetism is due to a certain occupation scheme of the orbitals from the parent octahedral t2g shell on CoII sites, in which the orbital accommodating the unpaired electron is orthogonal to the dz2 orbitals of the surrounding W ions. We investigate the stabilization of such an orbital configuration on the Co sites and find that it cannot be achieved in the ground state of isolated mononuclear fragments [CoII(NC)4(OH2)2]2- for any conformations of the coordinated water molecules and Co-N-C bond angles. On the other hand, it is stabilized by the interaction of the complex with neighboring W ions, which are simulated here by effective potentials. The calculated exchange coupling constants for the CoII-NC-WV binuclear fragments are in reasonable agreement with the measured Curie-Weiss constant for this compound. As additional evidence for the inferred electronic configuration on the Co sites, the ligand-field transitions, the temperature-dependent magnetic susceptibility, and the field-dependent low-temperature magnetization, simulated ab initio for the mononuclear Co fragments, are in agreement with the available data for another compound [WIV[(micro-CN)4-CoII(H2O)2]2.4H2O]n containing diamagnetic W and high-spin Co ions in an isostructural environment.
Study of the most relevant spin–orbit coupling descriptions of magnetic excitations in a series of lanthanide complexes
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D1CP05469D
Abstract: This study on spin-orbit coupling descriptions of magnetic excitations in lanthanide complexes compares the accuracy in crystal field energies and magnetic anisotropies calculated using different approximations to the Breit-Pauli spin-orbit Hamiltonian.
Double aromaticity and ring currents in open-shell systems
Publisher: Elsevier BV
Date: 12-2009
Ring-current signatures in shielding-density maps
Publisher: Elsevier BV
Date: 2005
A diatropic ring current in a fluorofullerene trannulene
Publisher: Royal Society of Chemistry (RSC)
Date: 2003
DOI: 10.1039/B307514C
Abstract: Ipsocentric current-density maps for a fluorofullerene derivative, C60F15H3, modelling the addition pattern of the experimentally characterised C60F15[CBr(CO2Et)2]3 which contains an [18]trans-annulene system, reveal a diamagnetic ring current dominated by the contribution of the four HOMO electrons, as in a classical (4n + 2) aromatic annulene.
Theoretical results which strengthen the hypothesis of electroweak bioenantioselection
Publisher: American Physical Society (APS)
Date: 03-1999
Counter-rotating spin-polarised ring currents in odd-electron carbocycles
Publisher: Wiley
Date: 06-12-2013
Abstract: We propose a molecular-orbital model to explain how majority and minority spins in odd-π-electron carbocycles sustain counter-rotating magnetic-field-induced ring currents. The model is based on the ipsocentric approach to magnetic response, in which ring currents are dominated by frontier-orbital contributions obeying angular-momentum selection rules. Coupled unrestricted Hartree-Fock ab initio calculations of the ring-current responses for singly charged benzene and planarised cyclo-octatetraene ions confirm the predictions of the qualitative model, and are consistent with correlated MP2 spin-polarised current calculations.
Aromaticity of strongly bent benzene rings: Persistence of a diatropic ring current and its shielding cone in [5]paracyclophane
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C1CP21950B
Abstract: Direct evaluation of the induced π current density in [5]paracyclophane (1) shows that, despite the significant non-planarity (α = 23.2°) enforced by the pentamethylene bridge, there is only a modest (ca. 17%) reduction in the π ring current, justifying the use of shielding-cone arguments for the assignment of (1)H NMR chemical shifts of 1 and the claim that the non-planar benzene ring in 1 retains its aromaticity (on the magnetic criterion).
Effect of magnetic anisotropy on direct chiral discrimination in paramagnetic NMR spectroscopy
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0CP00539H
Abstract: We have studied the effect of thermally populated crystal field states on room temperature chiral discrimination in NMR spectroscopy.
On the Stabilization of Natural l-α-Amino Acids and d-Sugars via Parity-Violating Effects
Publisher: Elsevier
Date: 1999
Metal Cluster Electrides: A New Type of Molecular Electride with Delocalised Polyattractor Character
Publisher: Wiley
Date: 13-06-2018
Abstract: Electrides are ionic substances containing isolated electrons. These confined electrons are topologically characterised by a quasi-atom, that is, a non-nuclear attractor (NNA) of the electron density. The electronic structure of the octahedral
Slow Magnetic Relaxation in Lanthanoid Crown Ether Complexes: Interplay of Raman and Anomalous Phonon Bottleneck Processes
Publisher: Wiley
Date: 17-09-2018
Abstract: The combination of lanthanoid nitrates with 18-crown-6 (18-c-6) and tetrahalocatecholate (X
The Leap-Frog Effect of Ring Currents in Benzene
Publisher: American Chemical Society (ACS)
Date: 05-02-2002
DOI: 10.1021/JA015952Z
Abstract: Symmetry arguments show that the ring-current model proposed by Pauling, Lonsdale, and London to explain the enhanced diamagnetism of benzene is flawed by an intrinsic drawback. The minimal basis set of six atomic 2p orbitals taken into account to develop such a model is inherently insufficient to predict a paramagnetic contribution to the perpendicular component of magnetic susceptibility in planar ring systems such as benzene. Analogous considerations can be made for the hypothetical H(6) cyclic molecule. A model allowing for extended basis sets is necessary to rationalize the magnetism of aromatics. According to high-quality coupled Hartree-Fock calculations, the trajectories of the current density vector field induced by a magnetic field perpendicular to the skeletal plane of benzene in the pi electrons are noticeably different from those typical of a Larmor diamagnetic circulation, in that (i) significant deformation of the orbits from circular to hexagonal symmetry occurs, which is responsible for a paramagnetic contribution of pi electrons to the out-of-plane component of susceptibility, and (ii) a sizable component of the pi current density vector parallel to the inducing field is predicted. This causes a waving motion of pi electrons streamlines are characterized by a "leap-frog effect".
Invariance of magnetic-field induced current density to a continuous transformation of the origin of the coordinate system
Publisher: Elsevier BV
Date: 04-2006
Design of annulene-within-an-annulene systems by the altanisation approach. A study ofaltan-[n]annulenes
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/C9CP06835J
Abstract: Computations on neutral and charged [ n ]annulenes confirm the general effectiveness of altanisation to design paratropic perimeter circulations. An extension of the design strategy is required for open-shell singlet species.
Inelastic Neutron Scattering Measurement of the Ground State Tunneling Gap in Tb and Ho Analogues of a Dy Field-Induced Single-Molecule Magnet
Publisher: American Chemical Society (ACS)
Date: 11-01-2023
NMR chemical shift as analytical derivative of the Helmholtz free energy
Publisher: AIP Publishing
Date: 05-02-2013
DOI: 10.1063/1.4789398
Abstract: We present a theory for the temperature-dependent nuclear magnetic shielding tensor of molecules with arbitrary electronic structure. The theory is a generalization of Ramsey's theory for closed-shell molecules. The shielding tensor is defined as a second derivative of the Helmholtz free energy of the electron system in equilibrium with the applied magnetic field and the nuclear magnetic moments. This derivative is analytically evaluated and expressed as a sum over states formula. Special consideration is given to a system with an isolated degenerate ground state for which the size of the degeneracy and the composition of the wave functions are arbitrary. In this case, the paramagnetic part of the shielding tensor is expressed in terms of the g and A tensors of the electron paramagnetic resonance spin Hamiltonian of the degenerate state. As an illustration of the proposed theory, we provide an explicit formula for the paramagnetic shift of the central lanthanide ion in endofullerenes Ln@C60, with Ln = Ce3+, Nd3+, Sm3+, Dy3+, Er3+, and Yb3+, where the ground state can be a strongly spin-orbit coupled icosahedral sextet for which the paramagnetic shift cannot be described by previous theories.
C6h-hexa-azahexaborine, [(CH)BN]6: Structure and magnetic properties of a proposed 18-electron aromatic ring
Publisher: Royal Society of Chemistry (RSC)
Date: 2001
DOI: 10.1039/B103929F
Radical-lanthanide ferromagnetic interaction in a
T
Publisher:
American Physical Society (APS)
Date:
23-02-2018
Publisher: American Physical Society (APS)
Date: 23-02-2018
Ab Initio Non-Covalent Crystal Field Theory for Lanthanide Complexes: A Multiconfigurational Non-Orthogonal Group Functions Approach
Publisher: American Chemical Society (ACS)
Date: 18-02-2020
DOI: 10.26434/CHEMRXIV.11858346.V1
Abstract: We present a non-orthogonal fragment ab initio methodology for the calculation of crystal field energy levels and magnetic properties in lanthanide complexes, implementing a systematic description of non-covalent contributions to metal-ligand bonding. The approach has two steps. In the first step, appropriate ab initio wavefunctions for the various ionic fragments (lanthanide ion and coordinating ligands) are separately optimized, accounting for the electrostatic influence of the surrounding environment, within various approximations. In the second and final step, the scalar relativistic (DKH2) electrostatic Hamiltonian of the whole molecule is represented on the basis of the optimized metal-ligand multiconfigurational non-orthogonal group functions (MC-NOGF), and reduced to an effective (2J+1)-dimensional non-orthogonal Configuration Interaction (CI) problem via L{\"o}wdin-partitioning. Within the proposed formalism, the projected Hamiltonian can be implemented to any desired order of perturbation theory in the fragment-localised excitations out of the degenerate space, and its eigenvalues and eigenfunctions are systematic approximations to the crystal field energies and wavefunctions. We present a preliminary implementation of the proposed MC-NOGF method to first-order degenerate perturbation theory within our own ab initio code CERES, and compare its performance both with the simpler non-covalent orthogonal ab initio approach Fragment Ab Initio Model Potential (FAIMP) approximation, and with the full CAHF/CASCI-SO method, accounting for metal-ligand covalency in a mean-field manner. We find that energies and magnetic properties for 44 complexes obtained via an iteratively optimized version of our MC-NOGF first-order non-covalent method, compare remarkably well to the full CAHF/CASCI-SO method including metal-ligand covalency, and are superior to the best purely electrostatic results achieved via an iteratively optimized version of the FAIMP approach.
Survival and extinction of delocalized ring currents in clamped benzenes.
Publisher: Royal Society of Chemistry (RSC)
Date: 31-10-2001
DOI: 10.1039/B106651J
Abstract: Direct visualisation of induced current density in cl ed benzenes 1-4 distinguishes between saturated cl ing groups, for which the central benzene ring retains a conventional diamagnetic ring current, and strongly interacting, unsaturated cl s, for which the central ring supports only the localised circulations expected of a 1,3,5-cyclohexatriene with fully fixed double bonds.
Lanthanide-Radical Magnetic Coupling in [LnPc2]0: Competing Exchange Mechanisms Captured via Ab Initio Multi-Reference Calculations
Publisher: Hapres
Date: 2020
DOI: 10.20900/QMR20200003
The Role of Magnetic Dipole—Dipole Coupling in Quantum Single-Molecule Toroics
Publisher: MDPI AG
Date: 23-05-2022
DOI: 10.3390/MAGNETOCHEMISTRY8050058
Abstract: For single-molecule toroics (SMTs) based on noncollinear Ising spins, intramolecular magnetic dipole–dipole coupling favours a head-to-tail vortex arrangement of the semi-classical magnetic moments associated with a toroidal ground state. However, to what extent does this effect survive beyond the semi-classical Ising limit? Here, we theoretically investigate the role of dipolar interactions in stabilising ground-state toroidal moments in quantum Heisenberg rings with and without on-site magnetic anisotropy. For the prototypical triangular SMT with strong on-site magnetic anisotropy, we illustrate that, together with noncollinear exchange, intramolecular magnetic dipole–dipole coupling serves to preserve ground-state toroidicity. In addition, we investigate the effect on quantum tunnelling of the toroidal moment in Kramers and non-Kramers systems. In the weak anisotropy limit, we find that, within some critical ion–ion distances, intramolecular magnetic dipole–dipole interactions, diagonalised over the entire Hilbert space of the quantum system, recover ground-state toroidicity in ferromagnetic and antiferromagnetic odd-membered rings with up to seven sites, and are further stabilised by Dzyaloshinskii–Moriya coupling.
Origin of the hysteresis of magnetoconductance in a supramolecular spin-valve based on a TbPc2 single-molecule magnet
Publisher: American Physical Society (APS)
Date: 29-09-2020
Angular momentum and spectral decomposition of ring currents: Aromaticity and the annulene model
Publisher: Springer Berlin Heidelberg
Date: 19-07-2005
DOI: 10.1007/B135830
Non-perturbative magnetic phenomena in closed-shell paramagnetic molecules
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B822262B
Abstract: By means of non-perturbative ab initio calculations, it is shown that paramagnetic closed-shell molecules are characterized by a strongly non-linear magnetic response, whose main feature consists of a paramagnetic-to-diamagnetic transition in a strong magnetic field. The physical origin of this phenomenon is rationalised on the basis of an analytical model based on molecular orbital theory. For the largest molecules considered here, the acepleiadylene dianion and the corannulene dianion, the transition field is of the order of 10(3) T, about one order of magnitude larger than the magnetic field strength currently achievable in experimental settings. However, our simple model suggests that the paramagnetic-to-diamagnetic transition is a universal property of paramagnetic closed-shell systems in strong magnetic fields, provided no singlet-triplet level crossing occurs for fields smaller than the critical transition field. Accordingly, fields weaker than 100 T should suffice to trigger the predicted transition for systems whose size is still well within the (medium-large) molecular domain, such as hypothetical antiaromatic rings with less than one hundred carbon atoms.
Toroidal quantum states in molecular spin-frustrated triangular nanomagnets with weak spin-orbit coupling: Applications to molecular spintronics
Publisher: American Physical Society (APS)
Date: 14-09-2018
Triggering single-molecule qubit spin dynamics via non-Abelian geometric phase effects
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D3CP02939E
Ring currents in large [4n + 2]-annulenes
Publisher: Royal Society of Chemistry (RSC)
Date: 2004
DOI: 10.1039/B311487B
Polyenes with maximum HOMO-LUMO gap
Publisher: Elsevier BV
Date: 07-2001
Perimeter effects on ring currents in polycyclic aromatic hydrocarbons: Circumcoronene and two hexabenzocoronenes
Publisher: Wiley
Date: 25-06-2003
Magnetic excitations in polyoxotungstate-supported lanthanoid single-molecule magnets: an inelastic neutron scattering and ab initio study
Publisher: American Chemical Society (ACS)
Date: 15-12-2016
DOI: 10.1021/ACS.INORGCHEM.6B02312
Abstract: Inelastic neutron scattering (INS) has been used to investigate the crystal field (CF) magnetic excitations of the analogs of the most representative lanthanoid-polyoxometalate single-molecule magnet family: Na
Nuclear spin-spin coupling density in molecules
Publisher: AIP Publishing
Date: 11-04-2003
DOI: 10.1063/1.1561871
Abstract: It is shown that nuclear spin-spin coupling in a molecule can be rationalized in terms of property density functions which depend on the position in three-dimensional space. The spin-spin coupling density surface, calculated as a table of values for a grid of coordinates on a plane through the molecular domain, yields a direct physical picture and offers a physical interpretation of the phenomenology, by showing the path whereby coupling takes place. The different role and the relative importance of the Fermi contact, spin-dipolar, and diamagnetic and paramagnetic spin-orbit mechanisms is readily assessed. The display of the spin-spin density reveals that the major contribution comes from the electrons close to the coupled nuclei. The economy of thinking achieved by the use of functions of three coordinates in real space, instead of n-electron wave functions depending on 3n coordinates in Hilbert space, is evident in the present case. The utility of spin-spin coupling densities has been discussed for the molecules of hydrogen fluoride, water, ammonia, and methane.
Complete spectrum of the infinite- U Hubbard ring using group theory
Publisher: AIP Publishing
Date: 14-05-2014
DOI: 10.1063/1.4875039
Abstract: We present a full analytical solution of the multiconfigurational strongly correlated mixed-valence problem corresponding to the N-Hubbard ring filled with N−1 electrons, and infinite on-site repulsion. While the eigenvalues and the eigenstates of the model are known already, analytical determination of their degeneracy is presented here for the first time. The full solution, including degeneracy count, is achieved for each spin configuration by mapping the Hubbard model into a set of Hückel-annulene problems for rings of variable size. The number and size of these effective Hückel annulenes, both crucial to obtain Hubbard states and their degeneracy, are determined by solving a well-known combinatorial enumeration problem, the necklace problem for N−1 beads and two colors, within each subgroup of the CN−1 permutation group. Symmetry-adapted solution of the necklace enumeration problem is finally achieved by means of the subduction of coset representation technique [S. Fujita, Theor. Chim. Acta 76, 247 (1989)], which provides a general and elegant strategy to solve the one-hole infinite-U Hubbard problem, including degeneracy count, for any ring size. The proposed group theoretical strategy to solve the infinite-U Hubbard problem for N−1 electrons is easily generalized to the case of arbitrary electron count L, by analyzing the permutation group CL and all its subgroups.
Ab initio non-covalent crystal field theory for lanthanide complexes: a multiconfigurational non-orthogonal group function approach
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D1CP05488K
Abstract: We present a multiconfigurational ab initio methodology based on non-orthogonal fragments, quantitatively exposing metal–ligand non-covalent interaction contributions to crystal field energy levels and magnetic properties in lanthanide complexes.
Aromaticity of organic heterocyclothiazenes and analogues
Publisher: American Chemical Society (ACS)
Date: 20-08-2004
DOI: 10.1021/JA046399Z
Abstract: Members of a series of carbon-poor sulfur-nitrogen heterocycles and polycycles are shown by direct ab initio ipsocentric calculation to support diatropic ring currents and hence to be aromatic on the basis of magnetic criteria. They include 7-cycles S(3)N(2)(CH)(2), S(3)N(3)(CH), and S(3)N(4) and 8-cycles S(2)N(4)(CH)(2) and S(2)N(2)(CH)(4), all with 10 pi electrons. The unknown trithiatetrazepine S(3)N(4) is predicted to be at least as aromatic as its known diaza and triaza homologues. Angular-momentum arguments show that the pi-electron-rich nature of (4n + 2) SN heterocycles is the key to their diatropic current. The Woodward dithiatetrazocine parent framework S(2)N(4)(CH)(2) supports a diatropic ring current, as does its analogue in which N and CH groups are formally exchanged. Formal expansion of (4n + 2)-pi carbocyclic systems by insertion of NSN motifs in every CC bond is predicted to lead to structures that support diatropic ring currents: explicit ab initio calculation of magnetic response predicts the 24-center, 30-pi-electron heterocycle S(6)N(12)(CH)(6), formally derived from benzene, to be aromatic on the basis of this criterion.
Which π-clamped conjugated monocycles exhibit ring currents?
Publisher: Royal Society of Chemistry (RSC)
Date: 2004
DOI: 10.1039/B401125B
Abstract: Quenching/survival of ring currents in pi-cl ed conjugated monocycles is controlled by the match or mismatch in parity between the frontier orbitals of the central pi-conjugated 4n+2/4n monocycle and those of the cl s. Changes in ring current are not primarily caused by bond alternation or 'Mills-Nixon' effects current and geometry changes on cl ing are both consequences of electronic structure.
Molecular spintronics using single-molecule magnets under irradiation
Publisher: American Physical Society (APS)
Date: 10-06-2019
Spin-communication channels between Ln(III) bis-phthalocyanines molecular nanomagnets and a magnetic substrate
Publisher: Springer Science and Business Media LLC
Date: 24-02-2016
DOI: 10.1038/SREP21740
Abstract: Learning the art of exploiting the interplay between different units at the atomic scale is a fundamental step in the realization of functional nano-architectures and interfaces. In this context, understanding and controlling the magnetic coupling between molecular centers and their environment is still a challenging task. Here we present a combined experimental-theoretical work on the prototypical case of the bis(phthalocyaninato)-lanthanide(III) (LnPc 2 ) molecular nanomagnets magnetically coupled to a Ni substrate. By means of X-ray magnetic circular dichroism we show how the coupling strength can be tuned by changing the Ln ion. The microscopic parameters of the system are determined by ab-initio calculations and then used in a spin Hamiltonian approach to interpret the experimental data. By this combined approach we identify the features of the spin communication channel: the spin path is first realized by the mediation of the external (5d) electrons of the Ln ion, keeping the characteristic features of the inner 4 f orbitals unaffected, then through the organic ligand, acting as a bridge to the external world.
NMR chemical shift in an electronic state with arbitrary degeneracy
Publisher: American Physical Society (APS)
Date: 16-08-2012
An efficient coupled Hartree–Fock computational scheme for parity-violating energy differences in enantiomeric molecules
Publisher: Elsevier BV
Date: 04-2002
Single-ion anisotropy and exchange coupling in cobalt(ii )-radical complexes: insights from magnetic and ab initio studies
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9SC00914K
Abstract: The exchange coupling has been elucidated for a pseudo -octahedral cobalt( ii ) ion and radical semiquinonate ligand in a highly spin–orbit coupled system.
Titanium(III) Member of the Family of Trigonal Building Blocks with Scorpionate and Cyanide Ligands.
Publisher: American Chemical Society (ACS)
Date: 17-01-2017
DOI: 10.1021/ACS.INORGCHEM.6B02643
Abstract: The titanium(III) cyanide compound [Et
Full spectral decomposition of ring currents
Publisher: American Chemical Society (ACS)
Date: 11-2006
DOI: 10.1021/JP063760Q
Abstract: Within the ipsocentric method for calculation of molecular magnetic response, projection of perturbed orbitals onto the virtual orbital space allows partition of induced current density into contributions from in idual virtual excitations between occupied and unoccupied orbitals, enabling detailed assignment of the origin of currents in, e.g., benzene, cyclooctatetraene, borazine, coronene, and corannulene. Whereas delocalized currents in benzene and planar cyclooctatetraene are described by transitions within the valence space, localized currents in the borazine pi system involve excitations outside the valence space.
Aromaticity of ring carbo-mers of [N]annulenes and [N]cycloalkanes
Publisher: Royal Society of Chemistry (RSC)
Date: 2008
DOI: 10.1039/B715389A
Abstract: Maps of current density induced by a perpendicular external magnetic field are calculated at the ipsocentric CTOCD-DZ/6-31G**//B3PW91/6-31G** level for ring carbo-mers of [N]-annulenes (closed-shell singlet states of C(3N)H, N = 3 to 7, with q = -1, 0, +1, 0, -1, respectively, and also the triplet ground state for N = 4) and of [N]-cycloalkanes (C(3N)H(qN), N = 3, 4, 5). Strong four-electron diatropic ring currents indicate conventional pi aromaticity for all the singlet and triplet carbo-[N]annulenes studied, with the exception of C(12)H(4), where instead the strong two-electron paratropic ring current is the signature of pi antiaromaticity. The carbo-[N]cycloalkanes (also known as [N]pericyclynes) show only localized pi currents, consistent with non-aromaticity. There is no indication of a 'homo-aromatic' ring current attributable to the in-plane pi orbitals of the inserted C2 units in any of the maps. Consequences for the interpretation of ELF (electron localisation function) populations are discussed.
Configuration-averaged 4f orbitals in ab initio calculations of low-lying crystal field levels in lanthanide(iii ) complexes
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6CP02325H
Abstract: We propose an ab initio method that simplifies the CASSCF/RASSI–SO approach for crystal field levels and magnetic properties of lanthanide complexes.
Ferrotoroidic ground state in a heterometallic {CrIIIDyIII 6} complex displaying slow magnetic relaxation
Publisher: Springer Science and Business Media LLC
Date: 18-10-2017
DOI: 10.1038/S41467-017-01102-5
Abstract: Toroidal quantum states are most promising for building quantum computing and information storage devices, as they are insensitive to homogeneous magnetic fields, but interact with charge and spin currents, allowing this moment to be manipulated purely by electrical means. Coupling molecular toroids into larger toroidal moments via ferrotoroidic interactions can be pivotal not only to enhance ground state toroidicity, but also to develop materials displaying ferrotoroidic ordered phases, which sustain linear magneto–electric coupling and multiferroic behavior. However, engineering ferrotoroidic coupling is known to be a challenging task. Here we have isolated a {Cr III Dy III 6 } complex that exhibits the much sought-after ferrotoroidic ground state with an enhanced toroidal moment, solely arising from intramolecular dipolar interactions. Moreover, a theoretical analysis of the observed sub-Kelvin zero-field hysteretic spin dynamics of {Cr III Dy III 6 } reveals the pivotal role played by ferrotoroidic states in slowing down the magnetic relaxation, in spite of large calculated single-ion quantum tunneling rates.
A full‐pivoting algorithm for the Cholesky decomposition of two‐electron repulsion and spin‐orbit coupling integrals
Publisher: Wiley
Date: 25-09-2017
DOI: 10.1002/JCC.25062
Abstract: A significant reduction in the computational effort for the evaluation of the electronic repulsion integrals (ERI) in ab initio quantum chemistry calculations is obtained by using Cholesky decomposition (CD), a numerical procedure that can remove the zero or small eigenvalues of the ERI positive (semi)definite matrix, while avoiding the calculation of the entire matrix. Conversely, due to its antisymmetric character, CD cannot be directly applied to the matrix representation of the spatial part of the two-electron spin-orbit coupling (2e-SOC) integrals. Here, we present a computational strategy to achieve a Cholesky representation of the spatial part of the 2e-SOC integrals, and propose a new efficient CD algorithm for both ERI and 2e-SOC integrals. The proposed algorithm differs from previous CD implementations by the extensive use of a full-pivoting design, which allows a univocal definition of the Cholesky basis, once the CD δ threshold is made explicit. We show that 2δ is the upper limit for the errors affecting the reconstructed 2e-SOC integrals. The proposed strategy was implemented in the ab initio program Computational Emulator of Rare Earth Systems (CERES), and tested for computational performance on both the ERI and 2e-SOC integrals evaluation. © 2017 Wiley Periodicals, Inc.
Quantum Toroidicity in Single-Molecule Toroics: A Unifying Model Based on Heisenberg Spin Rings
Publisher: Springer International Publishing
Date: 2022
Introduction to Single-Molecule Toroics
Publisher: Springer International Publishing
Date: 2022
Mixed d-f Block Single-Molecule Toroics
Publisher: Springer International Publishing
Date: 2022
The Origin of Nonmagnetic Kramers Doublets in the Ground State of Dysprosium Triangles: Evidence for a Toroidal Magnetic Moment
Publisher: Wiley
Date: 09-05-2008
Interpretation of vicinal spin–spin coupling constants in ethane via the current-density induced by nuclear magnetic dipoles
Publisher: Elsevier BV
Date: 06-2005
Maps of current density using density-functional methods
Publisher: AIP Publishing
Date: 15-08-2008
DOI: 10.1063/1.2969104
Abstract: The performance of several density-functional theory (DFT) methods for the calculation of current densities induced by a uniform magnetic field is examined. Calculations are performed using the BLYP and KT3 generalized-gradient approximations, together with the B3LYP hybrid functional. For the latter, both conventional and optimized effective potential (OEP) approaches are used. Results are also determined from coupled-cluster singles-and-doubles (CCSD) electron densities by a DFT constrained search procedure using the approach of Wu and Yang (WY). The current densities are calculated within the CTOCD-DZ2 distributed origin approach. Comparisons are made with results from Hartree-Fock (HF) theory. Several small molecules for which correlation is known to be especially important in the calculation of magnetic response properties are considered—namely, O3, CO, PN, and H2CO. As ex les of aromatic and antiaromatic systems, benzene and planarized cyclooctatetraene molecules are considered, with specific attention paid to the ring current phenomenon and its Kohn-Sham orbital origin. Finally, the o-benzyne molecule is considered as a computationally challenging case. The HF and DFT induced current maps show qualitative differences, while among the DFT methods the maps show a similar qualitative structure. To assess quantitative differences in the calculated current densities with different methods, the maximal moduli of the induced current densities are compared and integration of the current densities to yield shielding constants is performed. In general, the maximal modulus is reduced in moving from HF to B3LYP and BLYP, and further reduced in moving to KT3, OEP(B3LYP), and WY(CCSD). The latter three methods offer the most accurate shielding constants in comparison with both experimental and ab initio data and hence the more reliable route to DFT calculation of induced current density in molecules.
Communication: Paramagnetic NMR chemical shift in a spin state subject to zero-field splitting
Publisher: AIP Publishing
Date: 10-01-2013
DOI: 10.1063/1.4775809
Abstract: We derive a general formula for the paramagnetic NMR nuclear shielding tensor of an open-shell molecule in a pure spin state, subject to a zero-field splitting (ZFS). Our findings are in contradiction with a previous proposal. We present a simple application of the newly derived formula to the case of a triplet ground state split by an easy-plane ZFS spin Hamiltonian. When kT is much smaller than the ZFS gap, thus a single non-degenerate level is thermally populated, our approach correctly predicts a temperature-independent paramagnetic shift, while the previous theory leads to a Curie temperature dependence.
Elucidation of LMCT Excited States for Lanthanoid Complexes: A Theoretical and Solid-State Experimental Framework
Publisher: American Chemical Society (ACS)
Date: 23-08-2022
DOI: 10.1021/ACS.INORGCHEM.2C01985
Abstract: Photophysical and magnetic properties arising from both ground and excited states of lanthanoid ions are relevant for numerous applications. These properties can be substantially affected, both adversely and beneficially, by ligand-to-metal charge-transfer (LMCT) states. However, probing LMCT states remains a significant challenge in f-block chemistry, particularly in the solid state. Intriguingly, the europium compounds [Eu
Ipsocentric and allocentric methods of mapping induced current density
Publisher: Elsevier BV
Date: 09-2004
Ring currents in tangentially p-p bonded σ-aromatic systems
Publisher: American Chemical Society (ACS)
Date: 19-07-2006
DOI: 10.1021/JO060788P
Abstract: We report a theoretical study of ring systems that delocalize electrons in a cyclic array of p orbitals arranged tangentially in sigma-bonding fashion. Sigma-bonded arrays are compared to conventional pi-bonded analogues with respect to orbital symmetry and aromatic/antiaromatic behavior. In a one-to-one correspondence between pi and tangential molecular orbitals of a cycle, local rotation turns each pi to a tangential basis function, changing bonding interactions to antibonding and inverting the order of filling of molecular orbitals. The ipsocentric ring-current mapping approach is used to evaluate aromaticity on the magnetic criterion. As for conventional pi-ring currents, the sigma-ring current in tangential p-p bonded systems is dominated by the HOMO-LUMO transition, corresponding to circulation of four electrons in diatropic (4n + 2)-electron cycles but two in paratropic (4n)-electron cycles. The systems examined here utilize either C 2p or Si 3p orbitals for delocalization. Although interchangeable with C with respect to the fundamental orbital symmetry and ring-current rules, Si bonds at greater internuclear distances, a feature that allows easier design of potentially stable sigma-aromatic structures. Calculations show the wheel-like Si10C50H70 structure 6 as a stable, neutral aromatic molecule with a diatropic ring current following the sigma-bond path formed by Si 3p orbitals.
Mechanisms of spin-mixing instabilities in antiferromagnetic molecular wheels
Publisher: American Physical Society (APS)
Date: 16-08-2007
Single molecule magnetism in a family of mononuclear beta-diketonate lanthanide(III) complexes: rationalization of magnetic anisotropy in complexes of low symmetry
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3SC22300K
Aromatization of Fulvene by Complexation with Lithium
Publisher: American Chemical Society (ACS)
Date: 28-09-2010
DOI: 10.1021/OL102037E
Abstract: At the B3LYP/6-311++G(d,p) level, approach of a lithium atom to a face of the fulvene molecule leads to formation of a complex with binding energy 41 kcal/mol and significant ion-pair character. The fulvene moiety gains a delocalized aromatic cyclic π system, documented by the geometry-based aromaticity index HOMA, and a strong diatropic ring current, visualized by ipsocentric calculation of the π current-density, which leads to an "aromatic" NICS value of -11 ppm.
Paratropic delocalized ring currents in flattened cyclooctatetraene systems with bond alternation
Publisher: Wiley
Date: 02-05-2002
DOI: 10.1002/1521-3773(20020503)41:9<1558::AID-ANIE1558>3.0.CO;2-G
Molecular spintronics in mixed-valence magnetic dimers: The double-exchange blockade mechanism
Publisher: American Chemical Society (ACS)
Date: 21-05-2010
DOI: 10.1021/JA101887F
Abstract: We theoretically investigate the charge and spin transport through a binuclear Fe(III)Fe(III) iron complex connected to two metallic electrodes. During the transport process, the Fe(III)Fe(III) dimer undergoes a one-electron reduction (Coulomb blockade transport regime), leading to the reduced mixed-valence Fe(II) Fe(III) species. For such a system, the additional electron may be fully delocalized leading to the stabilization of the highest spin ground state S = 9/2 by the double exchange mechanism, while the original Fe(III)Fe(III) has usually an S = 0 spin ground state due to the antiferromagnetic exchange coupling between the two Fe(III) ions. Intuitively, the spin delocalization within the mixed-valence complex may be thought to favor charge and spin transport through the molecule between the two metallic electrodes. Contrary to such an intuitive concept, we find that the increased delocalization leads in fact to a blocking of the transport, if the exchange coupling interaction within the Fe(III)Fe(III) dimer is antiferromagnetic. This is due to the violation of the spin angular momentum conservation, where a change of half a unit of spin (DeltaS = 1/2) is allowed between two different redox states of the molecule. The result is explained in terms of a double-exchange blockade mechanism, triggered by the interplay between spin delocalization and antiferromagnetic coupling between the magnetic cores. Consequently, ferromagnetically coupled dimers are shown not to be affected by the double-exchange blockade mechanism. The situation is evocative of the onset and removal of giant magnetoresistance in the conductance of diamagnetic layers, as a function of the relative alignment of the magnetization of two weakly antiferromagnetically coupled ferromagnetic contacts. Numerical simulations accounting for the effect of vibronic coupling show that the spin current increases as a function of spin delocalization in Class I and Class II mixed-valence dimers. The signature of vibronic coupling on sequential spin-tunneling processes through Class I and Class II mixed-valence systems is identified and discussed.
CERES: An ab initio code dedicated to the calculation of the electronic structure and magnetic properties of lanthanide complexes
Publisher: Wiley
Date: 20-11-2018
DOI: 10.1002/JCC.25113
Abstract: We have developed and implemented a new ab initio code, Ceres (Computational Emulator of Rare Earth Systems), completely written in C++11, which is dedicated to the efficient calculation of the electronic structure and magnetic properties of the crystal field states arising from the splitting of the ground state spin-orbit multiplet in lanthanide complexes. The new code gains efficiency via an optimized implementation of a direct configurational averaged Hartree-Fock (CAHF) algorithm for the determination of 4f quasi-atomic active orbitals common to all multi-electron spin manifolds contributing to the ground spin-orbit multiplet of the lanthanide ion. The new CAHF implementation is based on quasi-Newton convergence acceleration techniques coupled to an efficient library for the direct evaluation of molecular integrals, and problem-specific density matrix guess strategies. After describing the main features of the new code, we compare its efficiency with the current state-of-the-art ab initio strategy to determine crystal field levels and properties, and show that our methodology, as implemented in Ceres, represents a more time-efficient computational strategy for the evaluation of the magnetic properties of lanthanide complexes, also allowing a full representation of non-perturbative spin-orbit coupling effects. © 2017 Wiley Periodicals, Inc.
Ring Currents and Magnetic Properties of s-Indacene, an Archetypal Paratropic, Non-Antiaromatic Molecule
Publisher: American Chemical Society (ACS)
Date: 08-11-2002
DOI: 10.1021/JP0263267
Current-density maps as probes of aromaticity: Global and Clar π ring currents in totally resonant polycyclic aromatic hydrocarbons
Publisher: Royal Society of Chemistry (RSC)
Date: 2007
DOI: 10.1039/B604769F
Abstract: Calculation and visualisation of induced current density are important aids to the study of both aromaticity and observable molecular magnetic response properties. The ipsocentric method offers an accurate and economical approach to calculation of induced current density, and a physical interpretation in terms of occupied-orbital contributions. In monocyclic systems, these contributions allow rationalisation of the existence, sense, and strength of ring current using simple symmetry and node-counting arguments. Here we show maps computed with the model pseudo-pi version of the ipsocentric theory for large polycyclic aromatic hydrocarbons (PAH) of the Clar type. Maps are presented for D(6h)-symmetric systems with up to 438 carbon centres a full ab initio calculation for an isomer of C114H30 confirms that the success of the pseudo-pi method for small PAH carries over to these larger systems. The computed maps follow a generic overall pattern that can be understood with a natural extension of the orbital arguments to a 'band theory' of totally resonant PAH. All show pi current densities that combine a Clar-sextet structure of localised benzenoid diatropic ring currents (contributed by just four HOMO electrons) with a global perimeter diatropic ring current contributed by the remaining pi electrons. Both currents are explained in the ipsocentric model: the localised currents arise from excitations from the HOMO the perimeter current from excitations from the rest of the HOMO-band.
Molecular response to a time-independent non-uniform magnetic-field
Publisher: Elsevier BV
Date: 10-2004
Room Temperature Chiral Discrimination in Paramagnetic NMR Spectroscopy
Publisher: American Physical Society (APS)
Date: 18-04-2016
A Unified Orbital Model of Delocalised and Localised Currents in Monocycles, from Annulenes to Azabora‐heterocycles
Publisher: Wiley
Date: 28-01-2005
Abstract: Why are some (4n+2)pi systems aromatic, and some not? The ipsocentric approach to the calculation of the current density induced in a molecule by an external magnetic field predicts a four-electron diatropic (aromatic) ring current for (4n+2)pi carbocycles and a two-electron paratropic (antiaromatic) current for (4n)pi carbocycles. With the inclusion of an electronegativity parameter, an ipsocentric frontier-orbital model also predicts the transition from delocalised currents in carbocycles to nitrogen-localised currents in alternating azabora-heterocycles, which rationalises the differences in (magnetic) aromaticity between these isoelectronic pi-conjugated systems. Ab initio valence-bond calculations confirm the localisation predicted by the naive model, and coupled-Hartree-Fock calculations give current-density maps that exhibit the predicted delocalised-to-localised/carbocycle-heterocycle transition.
Rare-gas insertion compounds of perfluorobenzene: Aromaticity of some unstable species
Publisher: AIP Publishing
Date: 31-10-2005
DOI: 10.1063/1.2069867
Abstract: Calculations on the novel argon insertion compounds C6F6Arn, n=1–6, where the argon atoms are inserted into the C–F bonds in perfluorobenzene, suggest that all possible species, with one to six inserted argon atoms, occupy minima on their respective potential energy surfaces. Ring-current plots using the ipsocentric model indicate that there is no disruption of the aromatic π system upon argon insertion, and consequently all insertion compounds are aromatic according to the magnetic criterion. The barrier height for decomposition of the single-insertion compound, C6F6Ar, into C6F6+Ar is 19.5kcal∕mol at HF∕6-311G** and 29.5kcal∕mol at B3LYP∕6-311G**, suggesting that, although clearly thermodynamically unstable, argon-perfluorobenzene insertion compounds may be stable kinetically. Preliminary calculations indicate that other rare gas-perfluorobenzene insertion compounds may also be metastable. Both C6F6Ne and C6F6He are predicted to occupy minima on their respective potential energy surfaces.
Control of the diatropic π ring current in strained benzenes: Effects of annelation with cyclopropa, cyclobuta, and cyclobutadieno clamping groups
Publisher: American Chemical Society (ACS)
Date: 04-06-2002
DOI: 10.1021/JO020091D
Abstract: Direct visualization of the pi current density maps of highly strained annelated benzenes containing cyclopropa, cyclobuta, and cyclobutadieno cl s, alone and in combination, using a reliable distributed-origin, coupled Hartree-Fock method, shows the robustness of the classical benzene diatropic pi ring current. When only saturated cl s are used, the benzene ring current is essentially unchanged. In contrast, annelation with one or more cyclobutadieno cl s disrupts the benzene ring current. Analysis of orbital contributions to the current density maps gives a unified account of these observations in terms of the nature of the HOMO-LUMO transition.
Nuclear spin–spin coupling density functions and the Fermi hole
Publisher: AIP Publishing
Date: 02-07-2003
DOI: 10.1063/1.1581255
Abstract: Nuclear spin–spin coupling density functions yield a three-dimensional picture of the interaction between two nuclear dipole moments mediated by electron spin density. A physical interpretation of the Fermi contact coupling density maps can be readily arrived at on account of the Fermi correlation between same-spin electrons as the mechanism whereby the spin polarization induced about one nucleus is transmitted to another nucleus coupled to it. It is shown that the Fermi hole density function, evaluated by an opportune choice of the reference electron, is characterized by morphological aspects very similar to those appearing in the plots of one- and two-bonds Fermi contact density functions. A comparison has been made for hydrogen fluoride, water, ammonia, and methane molecules at the Hartree–Fock level of theory. The results confirm the role of the Fermi correlation as the fundamental vehicle propagating nuclear-spin/electron-spin contact interaction, i.e., the process mainly responsible for nuclear spin–spin coupling. The plots of Fermi hole density show that the geminal H–H coupling would not be possible without the essential contribution of the spin density in the vicinity of the heavier nucleus. The combined use of Fermi contact density functions and Fermi hole distributions yields a very promising approach to the study of nuclear magnetic resonance coupling constants, and provides a sound physical basis for their interpretation.
Observation of the asphericity of 4f-electron density and its relation to the magnetic anisotropy axis in single-molecule magnets
Publisher: Springer Science and Business Media LLC
Date: 16-12-2019
DOI: 10.1038/S41557-019-0387-6
Abstract: The distribution of electrons in the 4f orbitals of lanthanide ions is often assigned a crucial role in the design of single-molecule magnets, which maintain magnetization in zero external field. Optimal spatial complementarity between the 4f-electron density and the ligand field is key to maximizing magnetic anisotropy, which is an important factor in the ability of lanthanide complexes to display single-molecule magnet behaviour. Here we have experimentally determined the electron density distribution in two dysprosium molecular complexes by interpreting high-resolution synchrotron X-ray diffraction with a multipole model. The ground-state 4f-electron density is found to be an oblate ellipsoid, as is often deduced from a simplified Sievers model that assumes a pure |±15/2> ground-state doublet for the lanthanide ion. The large equatorial asymmetry-determined by a model wavefunction-was found to contain considerable M
Visualising aromaticity of bowl-shaped molecules
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C1CP21931F
Abstract: Superposition of slices (planar maps of induced current density calculated within the ipsocentric pseudo-π model of electronic response to a magnetic field) gives a simple route to visual diagnosis of ring-current aromaticity in bowl-shaped molecules. Results are presented for currents in the recently synthesized indenocorannulene precursors of [60]fullerene.
Few-layered graphene growth by carbon implantation into polycrystalline nickel substrate
Publisher: IEEE
Date: 12-2012
Relay-Like Exchange Mechanism through a Spin Radical between TbPc2 Molecules and Graphene/Ni(111) Substrates
Publisher: American Chemical Society (ACS)
Date: 14-10-2016
Abstract: We investigate the electronic and magnetic properties of TbPc
Mechanisms of spin-charge conversion for the electrical readout of 4f quantum states in a TbPc2 single-molecule magnet spin transistor
Publisher: American Physical Society (APS)
Date: 31-07-2020
Response tensors for chiral discrimination in NMR spectroscopy
Publisher: Springer Science and Business Media LLC
Date: 12-2006
Charge and spin currents in open-shell molecules: A unified description of NMR and EPR observables
Publisher: American Chemical Society (ACS)
Date: 17-10-2007
DOI: 10.1021/CT700169H
Abstract: The theory of EPR hyperfine coupling tensors and NMR nuclear magnetic shielding tensors of open-shell molecules in the limit of vanishing spin-orbit coupling (e.g., for organic radicals) is analyzed in terms of spin and charge current density vector fields. The ab initio calculation of the spin and charge current density response has been implemented at the Restricted Open-Shell Hartree-Fock, Unrestricted Hartree-Fock, and unrestricted GGA-DFT level of theory. On the basis of this formalism, we introduce the definition of nuclear hyperfine coupling density, a scalar function of position providing a partition of the EPR observable over the molecular domain. Ab initio maps of spin and charge current density and hyperfine coupling density for small radicals are presented and discussed in order to illustrate the interpretative advantages of the newly introduced approach. Recent NMR experiments providing evidence for the existence of diatropic ring currents in the open-shell singlet pancake-bonded dimer of the neutral phenalenyl radical are directly assessed via the visualization of the induced current density.
Ab initio calculations as a quantitative tool in the inelastic neutron scattering study of a single-molecule magnet analogue
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5CC07541F
Abstract: Ab initio calculations of the electronic structure of Na 9 [Tb(W 5 O 18 ) 2 ] have allowed interpretation of the inelastic neutron scattering spectra, revealing the subtle relationship between molecular geometry and magnetic properties of two isostructural species.
Aromaticity, polarisability and ring current
Publisher: Elsevier BV
Date: 2004
Spin-Orbit Coupling Descriptions of Magnetic Excitations in Lanthanide Complexes
Publisher: American Chemical Society (ACS)
Date: 18-02-2020
DOI: 10.26434/CHEMRXIV.11858370.V1
Abstract: We present a number of computationally cost-effective approaches to calculate magnetic excitations (i.e. crystal field energies and magnetic anisotropies in the lowest spin-orbit multiplet) in lanthanide complexes. In particular, we focus on the representation of the spin-orbit coupling term of the molecular Hamiltonian, which has been implemented within the quantum chemistry package CERES using various approximations to the Breit-Pauli Hamiltonian. The approximations include the (i) bare one-electron approximation, (ii) atomic mean field and molecular mean field approximations of the two-electron term, (iii) full representation of the Breit-Pauli Hamiltonian. Within the framework of the CERES implementation, the spin-orbit Hamiltonian is always fully diagonalized together with the electron repulsion Hamiltonian (CASCI-SO) on the full basis of Slater determinants arising within the 4f ligand field space. For the first time, we make full use of the Cholesky decomposition of two-electron spin-orbit integrals to speed up the calculation of the two-electron spin-orbit operator. We perform an extensive comparison of the different approximations on a set of lanthanide complexes varying both the lanthanide ion and the ligands. Surprisingly, while our results confirm the need of at least a mean field approach to accurately describe the spin-orbit coupling interaction within the ground Russell-Saunders term, we find that the simple bare one-electron spin-orbit Hamiltonian performs reasonably well to describe the crystal field split energies and g tensors within the ground spin-orbit multiplet, which characterize all the magnetic excitations responsible for lanthanide-based single-molecule magnetism.
Toroidal moment in a family of spin-frustrated heterometallic triangular nanomagnets without spin-orbit coupling: Applications in a molecular spintronics device
Publisher: Elsevier BV
Date: 09-2020
Calculation of electric dipole hypershieldings at the nuclei in the Hellmann–Feynman approximation
Publisher: AIP Publishing
Date: 10-02-2004
DOI: 10.1063/1.1630016
Abstract: The third-rank electric hypershieldings at the nuclei of four small molecules have been evaluated at the Hartree–Fock level of theory in the Hellmann–Feynman approximation. The nuclear electric hypershieldings are closely related to molecular vibrational absorption intensities and a generalization of the atomic polar tensors (expanded in powers of the electric field strength) is proposed to rationalize these intensities. It is shown that the sum rules for rototranslational invariance and the constraints imposed by the virial theorem provide useful criteria for basis-set completeness and for near Hartree–Fock quality of nuclear shieldings and hypershieldings evaluated in the Hellmann–Feynman approximation. Twelve basis sets of different size and quality have been employed for the water molecule in an extended numerical test on the practicality of the proposed scheme. The best results are obtained with the R12 and R12+ basis sets, designed for the calculation of electronic energies by the explicitly correlated R12 method. The R12 basis set is subsequently used to investigate three other molecules, CO, N2, and NH3, verifying that the R12 basis consistently performs very well.
Saltational evolution of the heterotrimeric G protein signaling mechanisms in the plant kingdom
Publisher: American Association for the Advancement of Science (AAAS)
Date: 20-09-2016
DOI: 10.1126/SCISIGNAL.AAF9558
Abstract: Rapid ersification of the XLG family of Gα proteins may have enabled plants to adapt to the variable land environment.
Critique of the Multipath Model for 1J(C,C) Nuclear Spin–Spin Coupling via Electron Current Induced by 13C Nuclear Magnetic Dipoles
Publisher: Wiley
Date: 03-03-2006
Non-linear ring currents: Effect of strong magnetic fields on π-electron circulation
Publisher: Elsevier BV
Date: 12-2004
Ring currents in the porphyrins: π shielding, delocalisation pathways and the central cation
Publisher: Royal Society of Chemistry (RSC)
Date: 2005
DOI: 10.1039/B511913H
Abstract: It is shown that the ipsocentric orbital-based model explains how the charge of the central cation drives the delocalisation pathway in metalloporphyrins. A positive charge +Ze at the centre of the porphin ring gives rise to a two-way radial transfer of charge within the pi structure of the porphin macrocycle. This manifests itself in a change of pathway of the global pi current, as Z increases from Z = 0, from an inner- through a bifurcated- to an outer-pathway. Changes of pathway can be interpreted in terms of a specific pi shielding effect whereby electrons in high-lying pi orbitals are screened from the central charge by the electrons in lower-lying orbitals of the same symmetry. These changes in pi structure are essentially independent of accompanying changes in the sigma structure.
Carbonate-Bridged Lanthanoid Triangles: Single-Molecule Magnet Behavior, Inelastic Neutron Scattering, and Ab Initio Studies
Publisher: American Chemical Society (ACS)
Date: 20-05-2016
DOI: 10.1021/ACS.INORGCHEM.6B00108
Abstract: Optimization of literature synthetic procedures has afforded, in moderate yield, homogeneous and crystalline s les of the five analogues Na11[{RE(OH2)}3CO3(PW9O34)2] (1-RE RE = Y, Tb, Dy, Ho, and Er). Phase-transfer methods have allowed isolation of the mixed salts (Et4N)9Na2[{RE(OH2)}3CO3(PW9O34)2] (2-RE RE = Y and Er). The isostructural polyanions in these compounds are comprised of a triangular arrangement of trivalent rare-earth ions bridged by a μ3-carbonate ligand and sandwiched between two trilacunary Keggin {PW9O34} polyoxometalate ligands. Alternating-current (ac) magnetic susceptibility studies of 1-Dy, 1-Er, and 2-Er reveal the onset of frequency dependence for the out-of-phase susceptibility in the presence of an applied magnetic field at the lowest measured temperatures. Inelastic neutron scattering (INS) spectra of 1-Ho and 1-Er exhibit transitions between the lowest-lying crystal-field (CF) split states of the respective J = 8 and (15)/2 ground-state spin-orbit multiplets of the Ho(III) and Er(III) ions. Complementary ab initio calculations performed for these two analogues allow excellent reproduction of the experimental magnetic susceptibility and low-temperature magnetization data and are in reasonable agreement with the experimental INS data. The ab initio calculations reveal that the slight difference in coordination environments of the three Ln(III) ions in each complex gives rise to differences in the CF splitting that are not insignificant. This theoretical result is consistent with the observation of multiple relaxation processes by ac magnetic susceptibility and the broadness of the measured INS peaks. The ab initio calculations also indicate substantial mixing of the MJ contributions to the CF split energy levels of each Ln(III) ion. Calculations indicate that the CF ground states of the Ho(III) centers in 1-Ho are predominantly comprised of contributions from small MJ, while those of the Er(III) centers in 1-Er are predominantly comprised of contributions from large MJ, giving rise to slow magnetic relaxation. Although no direct evidence for intramolecular RE···RE magnetic coupling is observed in either magnetic or INS studies, on the basis of the ab initio calculations, we find noncollinear magnetic axes in 1-Er that are coplanar with the erbium triangle and radially arranged with respect to the triangle's centroid thus, we argue that the absence of magnetic coupling in this system arises from dipolar and antiferromagnetic superexchange interactions that cancel each other out.
Parity-violating effects in asymmetric chemical reactions: A theoretical study on the CHFClBr molecule
Publisher: American Physical Society (APS)
Date: 12-2000
Abstract: A coupled Hartree-Fock procedure has been employed to estimate the parity-violating energy contribution due to electroweak interaction in the vicinity of the transition point of a chemical reaction path starting from achiral reagents and producing the chiral CHFClBr molecule. The calculations demonstrate that (i) the S enantiomer is a reaction product more stable than its mirror image by approximately 1x10(-17) hartree (ii) in the transition state of the reaction, the chiral activated complex evolving toward the S-CHFClBr species is more stable, by approximately 2.3x10(-17) hartree, than the enantiomeric activated complex that would yield the R-CHFClBr species. These results suggest that kinetic effects at work during chemical syntheses of chiral molecules might be more significant than the different thermodynamical stability of the two mirror-image reaction products in determining the final configuration and to explain homochirality.
A parity rule for ring currents in π-clamped monocycles
Publisher: Royal Society of Chemistry (RSC)
Date: 2004
DOI: 10.1039/B414024A
Dirac cones in the spectrum of bond-decorated graphenes
Publisher: AIP Publishing
Date: 20-06-2014
DOI: 10.1063/1.4883489
Abstract: We present a two-band model based on periodic Hückel theory, which is capable of predicting the existence and position of Dirac cones in the first Brillouin zone of an infinite class of two-dimensional periodic carbon networks, obtained by systematic perturbation of the graphene connectivity by bond decoration, that is by inclusion of arbitrary π-electron Hückel networks into each of the three carbon–carbon π-bonds within the graphene unit cell. The bond decoration process can fundamentally modify the graphene unit cell and honeycomb connectivity, representing a simple and general way to describe many cases of graphene chemical functionalization of experimental interest, such as graphyne, janusgraphenes, and chlorographenes. Exact mathematical conditions for the presence of Dirac cones in the spectrum of the resulting two-dimensional π-networks are formulated in terms of the spectral properties of the decorating graphs. Our method predicts the existence of Dirac cones in experimentally characterized janusgraphenes and chlorographenes, recently speculated on the basis of density functional theory calculations. For these cases, our approach provides a proof of the existence of Dirac cones, and can be carried out at the cost of a back of the envelope calculation, bypassing any diagonalization step, even within Hückel theory.
PHI: A powerful new program for the analysis of anisotropic monomeric and exchange‐coupled polynuclear d‐ and f‐block complexes
Publisher: Wiley
Date: 05-02-2013
DOI: 10.1002/JCC.23234
Abstract: A new program, PHI, with the ability to calculate the magnetic properties of large spin systems and complex orbitally degenerate systems, such as clusters of d-block and f-block ions, is presented. The program can intuitively fit experimental data from multiple sources, such as magnetic and spectroscopic data, simultaneously. PHI is extensively parallelized and can operate under the symmetric multiprocessing, single process multiple data, or GPU paradigms using a threaded, MPI or GPU model, respectively. For a given problem PHI is been shown to be almost 12 times faster than the well-known program MAGPACK, limited only by available hardware.
Tuning the Ferrotoroidic Coupling and Magnetic Hysteresis in Double‐Triangle Complexes {Dy3MIIIDy3} via the MIII‐linker
Publisher: Wiley
Date: 23-12-2020
Front Cover: Tuning the Ferrotoroidic Coupling and Magnetic Hysteresis in Double‐Triangle Complexes {Dy3MIIIDy3} via the MIII‐linker (Eur. J. Inorg. Chem. 5
Publisher: Wiley
Date: 14-01-2021
Disentangling 4f -radical coupling and dissipative Landau-Zener quantum tunneling in a continuously measured single-ion magnet spin transistor
Publisher: American Physical Society (APS)
Date: 17-11-2021
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