Examining the impact of harmonic correlation on vibrational frequencies calculated in localized coordinates

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Abstract

Carefully choosing a set of optimized coordinates for performing vibrational frequency calculations can significantly reduce the anharmonic correlation energy from the self-consistent field treatment of molecular vibrations. However, moving away from normal coordinates also introduces an additional source of correlation energy arising from mode-coupling at the harmonic level. The impact of this new component of the vibrational energy is examined for a range of molecules, and a method is proposed for correcting the resulting self-consistent field frequencies by adding the full coupling energy from connected pairs of harmonic and pseudoharmonic modes, termed vibrational self-consistent field (harmonic correlation). This approach is found to lift the vibrational degeneracies arising from coordinate optimization and provides better agreement with experimental and benchmark frequencies than uncorrected vibrational self-consistent field theory without relying on traditional correlated methods.

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Hanson-Heine, M. W. D. (2015). Examining the impact of harmonic correlation on vibrational frequencies calculated in localized coordinates. Journal of Chemical Physics, 143(16). https://doi.org/10.1063/1.4934234

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