THEORETICAL MOLECULAR-STRUCTURES AND VIBRATIONAL FREQUENCIES FOR THE DIOXODIHALIDES OF CHROMIUM(VI) AND MOLYBDENUM(VI)

Density functional theory calculations are reported for the ground-sta te geometries and harmonic vibrational energies of MO2X2 (M = Cr, Mo; X = F, CI). Both local density approximation (LDA) and nonlocal genera lized gradient approximation (GGA) functionals were investigated using several different STO basis sets. Both LDA and GGA results using basi s sets of double-zeta plus polarization function quality yield bond le ngths and angles within about 0.02 angstrom and 3-degrees of experimen t. GGA vibrational energies are systematically predicted to be lower t han observed but only by about 5% and 8% for the Cr and Mo species, re spectively. The implications of these results for the complete ab init io estimation of zero point energies together with thermodynamic quant ities at experimentally accessible temperatures are discussed.