Efficient calculation of anharmonic vibrational spectra of large molecules with localized modes.

摘要: The analysis and interpretation of the vibrational spectra complex (bio)molecular systems, such as polypeptides proteins, requires support from quantum-chemical calculations. Such calculations are currently restricted to harmonic approximation. Here, we show how one main bottlenecks in calculations, evaluation potential energy surface, can be overcome by using localized modes instead commonly employed normal modes. We apply local self-consistent field (L-VSCF) configuration interaction (L-VCI) a cyclic water tetramer helical hexa-alanine peptide. results that use is equivalent used modes, but offers several advantages. First, faster convergence with respect excitation level observed L-VCI Second, provide reduced representation couplings between regular coupling pattern. This disregard significant number small two-mode potentials priori. Several approximations explored, single-point required evaluate surface significantly without introducing noticeable errors resulting spectra.