DENSITY-FUNCTIONAL THEORY CALCULATIONS OF MOLECULAR-STRUCTURES AND HARMONIC VIBRATIONAL FREQUENCIES USING HYBRID DENSITY FUNCTIONALS

Geometries and harmonic frequencies of CH4, NH3, H2O, HF, C2H2, C2H4, C2H6, HCN, CO, H2CO and CH3F are calculated via density functional the ory (DFT) using the ''hybrid'' density functionals ''Becke3-Lee-Yang-P arr'' and ''Becke3-Perdew86'' at the 6-31G and TZ2P basis set levels. At both basis set levels, the results are in better agreement with ex periment than those obtained via DFT using the LSDA and BLYP functiona ls and via the SCF and MP2 methodologies. At the TZ2P basis set level, the mean absolute deviation of predicted and experimental bond length s is 0.005 Angstrom for both hybrid functionals; at 6-31G it is 0.006 Angstrom. The mean absolute percentage deviation of predicted and exp erimental harmonic vibrational frequencies is 1.2% at TZ2P and 1.9-2.0 % at 6-31G.