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 theory (DFT) using the ''hybrid'' density functionals ''Becke3-Lee-Yang-Parr'' and ''Becke3-Perdew86'' at the 6-31G* and TZ2P basis set levels. At both basis set levels, the results are in better agreement with experiment than those obtained via DFT using the LSDA and BLYP functionals and via the SCF and MP2 methodologies. At the TZ2P basis set level, the mean absolute deviation of predicted and experimental bond lengths is 0.005 Angstrom for both hybrid functionals; at 6-31G* it is 0.006 Angstrom. The mean absolute percentage deviation of predicted and experimental harmonic vibrational frequencies is 1.2% at TZ2P and 1.9-2.0% at 6-31G*.