A vibrational analysis of the 7-azaindole-water complex: Anharmonicities using the quartic force field

摘要

Vibrational frequencies for the 7-azaindole and 7-azaindole-water complex are calculated by the vibrational self-consistent field (VSCF) and correlation-corrected VSCF (cc-VSCF) methods using second-order perturbation theory (MP2), with the 6-31G(d) basis set, and density functional theory with the B3LYP functional and the same basis set. The potential energies at quadrature points for VSCF calculations are estimated from the quartic force field (QFF) determined by the respective electronic structure methods. The comparison with experimental fundamentals for 7-azaindole indicates that MP2 gives better results for NH and CH stretching modes than B3LYP, while B3LYP gives better results for CC stretching and ring deforming modes. The vibrational modes for the 7-azaindole-water complex are discussed in terms of those of the isolated 7-azaindole and water. This VSCF/QFF approach will help quantitative evaluations of vibrational energies of a general polyatomic molecule with a reasonable computational cost. (c) 2005 Wiley Periodicals, Inc.