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Generalized Vibrational Perturbation Theory for Rotovibrational Energies of Linear, Symmetric and Asymmetric Tops: Theory, Approximations, and Automated Approaches to Deal with Medium-to-Large Molecular Systems.

Piccardo M, Bloino J, Barone V - Int J Quantum Chem (2015)

Bottom Line: Moreover, generalized (GVPT) strategies combining the use of perturbative and variational formalisms can be adopted to further improve the accuracy of the results, with the first approach used for weakly coupled terms, and the second one to handle tightly coupled ones.The computational strategies and approximations that can be adopted in dealing with GVPT computations are pointed out, with a particular attention devoted to the treatment of symmetry and degeneracies.A number of tests and applications are discussed, to show the possibilities of the developments, as regards both the variety of treatable systems and eligible methods.

View Article: PubMed Central - PubMed

Affiliation: Scuola Normale Superiore Piazza dei Cavalieri 7, I-56126, Pisa, Italy E-mail: vincenzo.barone@sns.it.

No MeSH data available.


Medium-sized symmetric top systems of interest.
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fig02: Medium-sized symmetric top systems of interest.

Mentions: Moving to larger systems, the importance of taking into account the anharmonicity appears clearly in Tables11 and 12. In the first Table, both the harmonic and anharmonic computational results for triphenylamine are compared with the observed frequencies. Triphenylamine has a D3 three-bladed propeller structure, with a planar central NCCC moiety (see Fig. 2), and has found applications in different fields, including for instance photoconductors and semiconductors.177–180 With 96 vibrational normal modes, the determination of the complete anharmonic force field for this system is computationally very expensive even at the DFT level. However, within the reduced-dimensionality approach, it is possible to calculate the anharmonic corrections for a small selection of vibrational energies of interest. If the harmonic energy of the latter are well separated from the energies of the vibrations ignored in the anharmonic treatment, the cubic and quartic forces involving normal modes of both sets can be assumed to be negligible. In Table 11, the anharmonic corrections have been applied to fundamental vibrational states having harmonic wavenumbers larger than 3000 cm−1 which correspond to the CH stretchings region. The calculation has been done at the B3LYP/6-31G* level, and the resonances have been treated with the DSPT2 method. In Table 11, the empirical fundamental frequencies, obtained scaling the B3LYP/AVTZ harmonic frequencies by a factor of 0.986 (see Ref.181), are also reported, together with the experimental results, measured by FTIR spectroscopy of triphenylamine monomers isolated in an argon matrix.181 The inclusion of anharmonic effects leads to a significantly better agreement between the theoretical and experimental results with respect to the scaled values.


Generalized Vibrational Perturbation Theory for Rotovibrational Energies of Linear, Symmetric and Asymmetric Tops: Theory, Approximations, and Automated Approaches to Deal with Medium-to-Large Molecular Systems.

Piccardo M, Bloino J, Barone V - Int J Quantum Chem (2015)

Medium-sized symmetric top systems of interest.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4553754&req=5

fig02: Medium-sized symmetric top systems of interest.
Mentions: Moving to larger systems, the importance of taking into account the anharmonicity appears clearly in Tables11 and 12. In the first Table, both the harmonic and anharmonic computational results for triphenylamine are compared with the observed frequencies. Triphenylamine has a D3 three-bladed propeller structure, with a planar central NCCC moiety (see Fig. 2), and has found applications in different fields, including for instance photoconductors and semiconductors.177–180 With 96 vibrational normal modes, the determination of the complete anharmonic force field for this system is computationally very expensive even at the DFT level. However, within the reduced-dimensionality approach, it is possible to calculate the anharmonic corrections for a small selection of vibrational energies of interest. If the harmonic energy of the latter are well separated from the energies of the vibrations ignored in the anharmonic treatment, the cubic and quartic forces involving normal modes of both sets can be assumed to be negligible. In Table 11, the anharmonic corrections have been applied to fundamental vibrational states having harmonic wavenumbers larger than 3000 cm−1 which correspond to the CH stretchings region. The calculation has been done at the B3LYP/6-31G* level, and the resonances have been treated with the DSPT2 method. In Table 11, the empirical fundamental frequencies, obtained scaling the B3LYP/AVTZ harmonic frequencies by a factor of 0.986 (see Ref.181), are also reported, together with the experimental results, measured by FTIR spectroscopy of triphenylamine monomers isolated in an argon matrix.181 The inclusion of anharmonic effects leads to a significantly better agreement between the theoretical and experimental results with respect to the scaled values.

Bottom Line: Moreover, generalized (GVPT) strategies combining the use of perturbative and variational formalisms can be adopted to further improve the accuracy of the results, with the first approach used for weakly coupled terms, and the second one to handle tightly coupled ones.The computational strategies and approximations that can be adopted in dealing with GVPT computations are pointed out, with a particular attention devoted to the treatment of symmetry and degeneracies.A number of tests and applications are discussed, to show the possibilities of the developments, as regards both the variety of treatable systems and eligible methods.

View Article: PubMed Central - PubMed

Affiliation: Scuola Normale Superiore Piazza dei Cavalieri 7, I-56126, Pisa, Italy E-mail: vincenzo.barone@sns.it.

No MeSH data available.