THE VIBRATIONAL FREQUENCIES OF CAO2, SCO2, AND TIO2 - A COMPARISON OFTHEORETICAL METHODS

The vibrational frequencies of several states of CaO2, ScO2, and TiO2 are computed using density functional theory (DFT), the Hartree-Fock a pproach, second-order Moller-Plesset perturbation theory (MP2), and th e complete-active-space self-consistent-field theory. Three different functionals are used in the DFT calculations, including two hybrid fun ctionals. The coupled cluster singles and doubles approach including t he effect of connected triples, determined using perturbation theory, is applied to selected stales. The Becke-Perdew 86 functional appears to be the most cost-effective method of choice, although even this fun ctional does not perform well for one stale of CaO2. The MP2 approach is significantly inferior to the DFT approaches.