Coupled-cluster and density functional calculations of the molecular structure, infrared spectra, Raman spectra, and harmonic force constants for methanol

Ab-initio CCSD(T)/6-311G(3df, 2p) calculations of the molecular structure and the harmonic force field of methanol were carried out to obtain high-level benchmark data. These results are compared with calculations based on the second-order Moller-Plesset, the Hartree-Fock (HF) and the non-local density functional methods, and with experimental results. Special attention has been paid to evaluation of methanol Raman intensities and depolarization ratios. The CCSD(T) force field was combined with the Cartesian polarizability derivatives calculated using the HF and the density functional (B-LYP) methods.