Basis Set Effects and the Choice of Reference Geometry in Ab Initio Calculations of Vibrational Spectra

摘要

A number of basis sets were evaluated for the computation of ab initio theoretical vibrational frequencies and infrared intensities. The question of whether a theoretical vibrational spectrum should be computed at experimental or theoretical molecular geometries was investigated in detail. The role of the way molecular correlation energy changes with geometry was shown to be the determining factor. This was examined for a series of test molecules, including several diatomics and the polyatomic species ethylene and methylenecyclopropene. Experimental geometries or ones computed including electron correlation effects yield the most accurate computed spectra for the cases studied. Keywords: Reprints, Ab initio calculations, Propenes, Basis sets, Vibrational spectra, Ethylradicals, Molecular structure. (MJM)