APPLICATION OF DENSITY FUNCTIONAL THEORY TO INFRARED-ABSORPTION INTENSITY CALCULATIONS ON TRANSITION-METAL CARBONYLS

Approximate density functional theory has been evaluated as a practical tool for calculations on infrared vibrational frequencies and absorption intensities of transition-metal complexes. The density functional schemes included the local density approximation (LDA) by Gunnarson (Phys. Rev. 1974, BIO, 1319) as well as a self-consistent nonlocal density functional method (LDA/NL) in which the gradient-corrected exchange term by Becke (Phys. Rev. 1988, A38, 3098) and the gradient-corrected correlation term by Perdew (Phys. Rev. 1986, B33, 8822) have been added to LDA. The LDA and LDA/NL schemes have been applied to calculations on the infrared vibrational frequencies and absorption intensities of Ni(CO)4 and Cr(CO)6. The calculations were carried out with a double-zeta plus polarization basis set for C and O and aa triple-zeta plus polarization basis set for Cr and Ni. The simple theoretical LDA-model has been found to reproduce vibrational spectra of metal carbonyls adequately. The more sophisticated, and also more expensive, nonlocal scheme does not introduce important improvements in the calculated vibrational frequencies for Cr(CO)6 and Ni(CO)4. The calculated frequencies are in general in better agreement with experiment than values obtained by ab initio Hartree-Fock calculations. Calculated atomic polar tensors and harmonic force fields are provided for both molecules.