A LOCAL DENSITY FUNCTIONAL-STUDY OF THE STRUCTURE AND VIBRATIONAL FREQUENCIES OF MOLECULAR TRANSITION-METAL COMPOUNDS

Local density functional (LDF) theory has been used to calculate the geometry and vibrational frequencies of a set transition-metal compounds in their molecular forms containing halogens, oxygens, alkyl groups, carbonyls, nitrosyls, and other substituents. The calculations were done with polarized double-zeta numerical and Gaussian basis sets, and the geometries were obtained by analytic gradient methods. The frequencies were evaluated by numerical differentiation of the analytic first derivatives. The results obtained with the numerical and the Gaussian basis sets were found to be in good agreement. The agreement with experiment for the geometries is quite good with an average mean deviation of 0.026 angstrom. The largest errors involve dative bonds with the LDF method predicting the bonds to be too short. Nonlocal corrections were applied to some of the methyl-carbonyl and metal-nitrosyl bond lengths, and this correction was found to lengthen the bonds to give better agreement with experiment. The frequencies are also predicted quite accurately. The LDF results are in much better agreement with experiment as compared to Hartree-Fock results.