Development and Implementation of Advanced Fitting Methods for the Calculation of Accurate Molecular Structures

Mendolicchio, Marco; Penocchio, Emanuele; Licari, Daniele; Tasinato, Nicola; Barone, Vincenzo

doi:10.1021/acs.jctc.7b00279

Cited by 60 publications

(83 citation statements)

References 88 publications

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“…In analogy to rotational constants, the equilibrium moment of inertia, straightforwardly derived from the CCSD(T)/CBS+CV geometry, has been corrected for the vibrational contribution at the B2PLYP-D3BJ/maug-cc-pVTZ-d H level. More precisely, in order to obtain the e↵ective I ↵ corresponding to the vibrational ground state, a least-squares fit of the moments of inertia of all mono-substituted isotopic species of CH 3 CHNH, evaluated by combining the equilibrium and vibrational contributions, has been carried out with the MSR software (Mendolicchio et al 2017). The effective I ↵ corresponds to the so-called vibrationally averaged structure r 0 (Gordy & Cook 1984).…”

Section: Computational Methodologymentioning

confidence: 99%

Rotational and Infrared Spectroscopy of Ethanimine: A Route toward Its Astrophysical and Planetary Detection

Melli

Melosso

Tasinato

et al. 2018

ApJ

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This%is%the%final%accepted%manuscript%of:% % A.% Melli,% M.% Melosso,% N.% Tasinato,% et% al.% ROTATIONAL% AND% INFRARED% SPECTROSCOPY% OF% ETHANIMINE:%A%ROUTE%TOWARDS%ITS%ASTROPHYSICAL%AND%PLANETARY%DETECTION.%Astrophys.%J.% 855,%123%(2018);%DOI:%10.3847/1538U4357/aaa899% % Available%at:%https://doi.org/10.3847/1538U4357/aaa899% % ABSTRACTEthanimine, a possible precursor of amino acids, is considered an important prebiotic molecule and thus may play important roles in the formation of biological building-blocks in the interstellar medium. In addition, its identification in Titan's atmosphere would be important for understanding the abiotic synthesis of organic species. An accurate computational characterization of the molecular structure, energetics and spectroscopic properties of the E and Z isomers of ethanimine, CH 3 CHNH, has been carried out by means of a composite scheme based on coupled-cluster techniques, which also accounts for extrapolation to the complete basis-set limit and core-valence correlation correction, combined with density functional theory for the treatment of vibrational anharmonic e↵ects. By combining the computational results with new millimeter-wave measurements up to 300 GHz, the rotational spectrum of both isomers can be accurately predicted up to 500 GHz. Furthermore, our computations allowed us to revise the infrared spectrum of both E -and Z -CH 3 CHNH, thus predicting all fundamental bands with high accuracy.

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Section: Computational Methodologymentioning

confidence: 99%

Rotational and Infrared Spectroscopy of Ethanimine: A Route toward Its Astrophysical and Planetary Detection

Melli

Melosso

Tasinato

et al. 2018

ApJ

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“…For a detailed account, the reader is referred to Ref. 16 A key issue is thus the evaluation of accurate structural parameters to be either kept fixed in the fitting procedure or used as predicates. The so-called template approach 15 has been introduced to further extend the size of molecular systems amenable to highly accurate molecular structure determinations.…”

Section: The Semi-experimental Approachmentioning

confidence: 99%

Diving for Accurate Structures in the Ocean of Molecular Systems with the Help of Spectroscopy and Quantum Chemistry

Puzzarini

Barone

2018

Acc. Chem. Res.

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The prediction and interpretation of structural properties are the starting points for a deep understanding of thermochemistry, kinetics, and spectroscopic signatures of molecular systems. To give an example, detailed knowledge of the conformational behavior of the main building blocks of biomolecules in the gas phase (i.e., without the perturbing effect of the environment) is a mandatory prerequisite toward the understanding of the role played by different interactions in determining the biological activity in terms of structure-activity relationships. The first step to take is an unambiguous definition of molecular structure. We address the so-called Born-Oppenheimer equilibrium structure, which is defined in a rigorous manner and isotopically independent, and the target accuracy. For the latter, we aim at so-called "spectroscopic" accuracy, which implies uncertainties of a few milliangstroms for bond lengths and smaller than a tenth of degree for angles. If on one side the continuous enhancements of the experimental techniques give access to new and unprecedented spectroscopic determinations, on the other side they require increasing efforts for an unbiased interpretation and analysis. Among the pieces of information, accurate molecular structures play a particularly important role. Indeed, there is a strong relationship between the experimental outcome and the electronic structure of the system. Spectroscopic techniques, in particular those exploited in the gas phase, are therefore accurate and reliable sources for structural information. However, it is seldom straightforward to derive molecular structures directly from the experimental information. Indeed, even in the favorable case of investigations in the gas phase, vibrational effects are always present, and disentangling their contributions requires collection of information for all vibrational modes, a nearly impossible task. To overcome these limitations, joint theory-spectroscopy strategies can be identified, which are referred to as "top-down" and "bottom-up". The first approach, denoted as the semiexperimental approach, relies on extracting from experimental outcomes the equilibrium structure by using quantum-chemical computations to recover vibrational effects. The bottom-up approach consists in verifying the computed equilibrium geometry by means of a comparison between calculated and experimental spectroscopic parameters that probe structural characteristics. In this contribution, we try to review the most important challenges in accurate molecular structure determinations, with particular emphasis on the "solution" provided by a joint theoretical-experimental approach and on the current state of the art. Starting from the illustration of different strategies, we proceed by addressing the increasing complexity in the derivation of equilibrium geometries: we start from the construction of a database of accurate structures, we then face the problem of extending the dimension of the systems amenable to accurate structural determinations, and finally...

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“…Indeed, experimental ES geometries are available for a small number of compact (typically two to six atoms) fluorescent derivatives only, contrasting with the plethora of available GS structures, that can now be accurately determined with advanced approaches combining theory and experiment. 15 More importantly, the experimental determinations of ES structures often imply quite large error bars and the values of some parameters have to be assumed or frozen during the fitting procedures. Therefore, assessing the accuracy of a particular theory using experimental ES structures is de facto not a very satisfying approach.…”

Section: Introductionmentioning

confidence: 99%

Accurate Excited-State Geometries: A CASPT2 and Coupled-Cluster Reference Database for Small Molecules

Budzák

Scalmani²,

Jacquemin

2017

J. Chem. Theory Comput.

166

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We present an investigation of the excited-state structural parameters determined for a large set of small compounds with the dual goals of defining reference values for further works and assessing the quality of the geometries obtained with relatively cheap computational approaches. In the first stage, we compare the excited-state geometries obtained with ADC(2), CC2, CCSD, CCSDR(3), CC3, and CASPT2 and large atomic basis sets. It is found that CASPT2 and CC3 results are generally in very good agreement with one another (typical differences of ca. 3 × 10–3 Å) when all electrons are correlated and when the aug-cc-pVTZ atomic basis set is employed with both methods. In a second stage, a statistical analysis reveals that, on the one hand, the excited-state (ES) bond lengths are much more sensitive to the selected level of theory than their ground-state (GS) counterparts and, on the other hand, that CCSDR(3) is probably the most cost-effective method delivering accurate structures. Indeed, CCSD tends to provide too compact multiple bond lengths on an almost systematic basis, whereas both CC2 and ADC(2) tend to exaggerate these bond distances, with more erratic error patterns, especially for the latter method. The deviations are particularly marked for the polarized CO and CN bonds, as well as for the puckering angle in formaldehyde homologues. In the last part of this contribution, we provide a series of CCSDR(3) GS and ES geometries of medium-sized molecules to be used as references in further investigations.

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Development and Implementation of Advanced Fitting Methods for the Calculation of Accurate Molecular Structures

Cited by 60 publications

References 88 publications

Rotational and Infrared Spectroscopy of Ethanimine: A Route toward Its Astrophysical and Planetary Detection

Rotational and Infrared Spectroscopy of Ethanimine: A Route toward Its Astrophysical and Planetary Detection

Diving for Accurate Structures in the Ocean of Molecular Systems with the Help of Spectroscopy and Quantum Chemistry

Accurate Excited-State Geometries: A CASPT2 and Coupled-Cluster Reference Database for Small Molecules

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