Vibrational corrections to hyperpolarizabilities of the O3, SO2, N2O and CO2 molecules: A comparison between variational and perturbation methods

In this work we reported results of vibrational corrections to the first and second hyperpolarizabilities of the O3, SO2, N2O and CO2 molecules at the CCSD level through the BKPT method of Bishop and Kirtman and also using a variational approximation proposed in a previous work. Comparison between results obtained by both methods shows that the performance of BKPT is different for the systems studied here. Practically the same results are obtained for sulfur dioxide while ozone is the system for which there is greater discrepancy between the results obtained by the two procedures.