ORCID Profile
0000-0003-3916-9850
Current Organisation
UNSW Sydney
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Publisher: Frontiers Media SA
Date: 08-04-2021
DOI: 10.3389/FSPAS.2021.639068
Abstract: Phosphine is now well-established as a biosignature, which has risen to prominence with its recent tentative detection on Venus. To follow up this discovery and related future exoplanet biosignature detections, it is important to spectroscopically detect the presence of phosphorus-bearing atmospheric molecules that could be involved in the chemical networks producing, destroying or reacting with phosphine. We start by enumerating phosphorus-bearing molecules (P-molecules) that could potentially be detected spectroscopically in planetary atmospheres and collecting all available spectral data. Gaseous P-molecules are rare, with speciation information scarce. Very few molecules have high accuracy spectral data from experiment or theory instead, the best current spectral data was obtained using a high-throughput computational algorithm, RASCALL, relying on functional group theory to efficiently produce approximate spectral data for arbitrary molecules based on their component functional groups. Here, we present a high-throughput approach utilizing established computational quantum chemistry methods (CQC) to produce a database of approximate infrared spectra for 958 P-molecules. These data are of interest for astronomy and astrochemistry (importantly identifying potential ambiguities in molecular assignments), improving RASCALL's underlying data, big data spectral analysis and future machine learning applications. However, this data will probably not be sufficiently accurate for secure experimental detections of specific molecules within complex gaseous mixtures in laboratory or astronomy settings. We chose the strongly performing harmonic ωB97X-D/def2-SVPD model chemistry for all molecules and test the more sophisticated and time-consuming GVPT2 anharmonic model chemistry for 250 smaller molecules. Limitations to our automated approach, particularly for the less robust GVPT2 method, are considered along with pathways to future improvements. Our CQC calculations significantly improve on existing RASCALL data by providing quantitative intensities, new data in the fingerprint region (crucial for molecular identification) and higher frequency regions (overtones, combination bands), and improved data for fundamental transitions based on the specific chemical environment. As the spectroscopy of most P-molecules have never been studied outside RASCALL and this approach, the new data in this paper is the most accurate spectral data available for most P-molecules and represent a significant advance in the understanding of the spectroscopic behavior of these molecules.
Publisher: CSIRO Publishing
Date: 2020
DOI: 10.1071/CH19466
Publisher: Wiley
Date: 23-10-2022
DOI: 10.1002/WCMS.1584
Abstract: Vibrational frequency calculations performed under the harmonic approximation are widespread across chemistry. However, it is well‐known that the calculated harmonic frequencies tend to systematically overestimate experimental fundamental frequencies a limitation commonly overcome with multiplicative scaling factors. In practice, multiplicative scaling factors are derived for each in idual model chemistry choice (i.e., a level of theory and basis set pair), where performance is judged by, for ex le, the root‐mean square error (RMSE) between the predicted scaled and experimental frequencies. However, despite the overwhelming number of scaling factors reported in the literature and model chemistry approximations available, there is little guidance for users on appropriate model chemistry choices for harmonic frequency calculations. Here, we compile and analyze the data for 1495 scaling factors calculated using 141 levels of theory and 109 basis sets. Our meta‐analysis of this data shows that scaling factors and RMSE approach convergence with only hybrid functionals and double‐zeta basis sets, with anharmonicity error already dominating model chemistry errors. Noting inconsistent data and the lack of independent testing, we can nevertheless conclude that a minimum error of 25 cm −1 —arising from insufficiently accurate treatment of anharmonicity—is persistent regardless of the model chemistry choice. Based on the data we compiled and cautioning the need for a future systematic benchmarking study, we recommend ω B97X‐D/def2‐TZVP for most applications and B2PLYP/def2‐TZVPD for superior intensity predictions. With a smaller benchmark set, direct comparison prefers ω B97X‐D/6‐31G* to B3LYP/6‐31G*. This article is categorized under: Electronic Structure Theory Density Functional Theory Theoretical and Physical Chemistry Spectroscopy
Publisher: American Chemical Society (ACS)
Date: 24-08-2020
No related grants have been discovered for Juan Camilo Zapata Trujillo.