The vibrational frequencies of CaO2, ScO2, and TiO2:: a comparison of theoretical methods

The vibrational frequencies of several states of CaO2, ScO2, and TiO2 are computed using density functional theory (DFT), the Hartree-Fock approach, second-order Moller-Plesset perturbation theory (MP2), and the complete-active-space self-consistent-field theory. Three different functionals are used in the DFT calculations, including two hybrid functionals. The coupled cluster singles and doubles approach including the 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 functional does not perform well for one stale of CaO2. The MP2 approach is significantly inferior to the DFT approaches.