Quantum Mechanical Molecular Force Fields Research Articles

Predictive abilities of scaled quantum mechanical molecular force fields: application to 2,3-dimethylbuta-1,3-diene

In connection with the appearance of new experimental vibrational data on the high-energy rotational isomer of 2,3-dimethylbuta-1,3-diene (I) in a low-temperature matrix and in neat crystals, the ab initio-based vibrational analysis of this molecule has been re-evaluated. Calculated wavenumbers derived from a scaled quantum-mechanical force field analysis at the MP2(FC)/aug-cc-pVDZ//MP2(FC)/aug-cc-pVDZ computational level are compared with experimental data. Several reassignments of the fundamental wavenumbers for I have been suggested in the course of the current analysis, and the existence of a high-energy non-planar s-gauche conformer of 2,3-dimethylbuta-1,3-diene has been confirmed.

Predictive abilities of scaled quantum-mechanical molecular force fields: application to 2-methylbuta-1,3-diene (isoprene)

The ab initio-based, scaled quantum-mechanical molecular force field (SQM-FF) analysis of the vibrational spectra of the s-trans and s-gauche conformers of 2-methylbuta-1,3-diene (isoprene), reported previously at the HF/6-31G//HF/6-31G computational level [Bock, et al. J Mol Struct 160: 337, 1987], has been updated in this article using a more complete set of experimental data on the s-gauche conformer along with revised results for the s-trans conformer obtained in the gas phase, in a low-temperature matrix, and in neat crystals. Geometrical parameters and the calculated wavenumbers derived from the SQM-FF at the MP2(FC)/aug-cc-pVDZ//MP2(FC)/aug-cc-pVDZ level are compared to experiment. The analyses performed are consistent with the presence of a twisted high-energy s-gauche conformer of isoprene.

Some aspects of scaling factor calculations for quantum-mechanical molecular force fields

Stages of the scaling procedure for correcting molecular force fields obtained in rough quantum chemical calculations are discussed. The procedure includes selection of the number of scaling factors and their determination using experimental vibration frequencies of isotopomers and related molecules. It is stated that the difference in anharmonicity corrections for light molecules and their heavy analogs is to be taken into account along with possible errors in vibration frequency assignments of both isotopomers and more complex related molecules.

Some Aspects of the Implementation of Scaling Quantum Mechanical Molecular Force Fields

Some features of software implementation of the Pulay scaling procedure are considered. The advantages of the single value decomposition method for maintaining well-conditionality of the scale factor determination problem are demonstrated. The necessity of using a rational number of scale factors is shown. The possibility of obtaining transferable scale factors with the Pulay method and thus predict the vibrational spectra of related compounds is emphasized.

Vibrational spectra and scaled quantum-mechanical molecular force fields

A number of questions connected with the use of scaled quantum-mechanical force fields in interpreting molecular vibrational spectra are considered briefly.The Pulay method of scaling (congruent transformation of the force constant matrix) is noted to be applicable in the case where the relative accuracies of the determination of diagonal and off-diagonal quantum-mechanical force constants are approximately equal. This requirement is satisfied for a quantum-mechanical force field determined close to the Hartree–Fock limit. Then it is possible to carry out its correction, preserving to a maximum the features inherent to the molecule under investigation.Several examples of predicting the vibrational spectra of isotopomers, rotational isomers, and related compounds are given. Unlike using force fields obtained by the traditional method of solving the inverse vibrational problem and the additive scheme for transferring the force constants, scaled quantum-mechanical force fields make it possible to perform well-grounded theoretical vibrational analyses of all the related compounds of a molecule.

Methods of scaling quantum mechanical molecular force fields

A comparative analysis of various methods of empirical scaling of the quantum mechanical harmonic molecular force fields has been performed. The Pulay method of scaling is stressed to be applicable most successfully in the case where the quantum mechanical force field is determined close to the Hartree-Fock limit. This makes it possible to carry out correction of this force field with maximal retention of the peculiarities inherent in the molecule under investigation.

Scaling of quantum-mechanical molecular force fields

Comparative analysis of various methods of empirical scaling of quantum-mechanical harmonic molecular force fields has been performed. The efficiency of using each particular scaling technique was shown to depend on the theoretical level of the quantum-mechanical calculation. The Pulay method of scaling (congruent transformation of the force constant matrix) is applicable in the case where the relative accuracies of determination of diagonal and off-diagonal quantum-mechanical force constants are approximately equal. This requirement is satisfied for a quantum-mechanical force field determined close to the HartreeFock limit. This makes it possible to carry out its correction with maximum retention of the peculiarities inherent in the molecule under investigation.

Some aspects of scaling the molecular quantum mechanical force field

Some aspects of the scaling method for empirical correction of theoretical quantum mechanical molecular force fields are considered. These are: (i) simultaneous scaling of the kinematic coefficient matrix and the force constant matrix, (ii) dependence of the force field, vibrational frequencies and modes on the scale factor matrix and (iii) the upper and lower estimations of derivatives of the frequencies with respect to scale factors. The conclusion is drawn that the advantages of the scaling procedure are most pronounced when it is applied to a quantum mechanical force field calculated at a level near the Hartree-Fock limit.

Testing the Validity of Scaling the Quantum Mechanical Molecular Force Fields for Rotational Isomers

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTTesting the Validity of Scaling the Quantum Mechanical Molecular Force Fields for Rotational IsomersYurii N. Panchenko, George R. De Maré, and Vladimir I. PupyshevCite this: J. Phys. Chem. 1996, 100, 26, 11202Publication Date (Web):June 27, 1996Publication History Published online27 June 1996Published inissue 1 January 1996https://doi.org/10.1021/jp961132aCopyright © 1996 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views146Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (86 KB) Get e-Alerts

Testing the Validity of Scaling the Quantum Mechanical Molecular Force Fields for Rotational Isomers

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTesting the Validity of Scaling the Quantum Mechanical Molecular Force Fields for Rotational IsomersYurii N. Panchenko, George R. De Mare, and Vladimir I. PupyshevCite this: J. Phys. Chem. 1995, 99, 49, 17544–17550Publication Date (Print):December 1, 1995Publication History Published online1 May 2002Published inissue 1 December 1995https://doi.org/10.1021/j100049a013RIGHTS & PERMISSIONSArticle Views53Altmetric-Citations28LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (837 KB) Supporting Info (3)»Supporting Information Supporting Information Get e-Alerts