The performance of explicitly correlated wavefunctions [CCSD(T)-F12b] in the computation of anharmonic vibrational frequencies

CCSD(T)-F12b/cc-pVTZ-F12 anharmonic vibrational frequencies match experiment or higher-level theory to within an average of 10.3 cm−1 for a sample set of 11 molecules. This is further reduced below 7.0 cm−1 when extreme differences are removed from the data set. CCSD(T)-F12b/cc-pVTZ-F12 and CCSD(T)-F12b/cc-pVDZ-F12 frequencies differ on average by 4.8 cm−1. The CCSD(T)-F12b frequencies require orders of magnitude less computer time than higher-order theory and cc-pVDZ-F12 less than cc-pVTZ-F12, especially as the number of atoms increases. Hence, utilization of these levels of theory may provide accurate vibrational frequencies for larger molecules provided that the core-electron correlation is not significant.