Vibrational corrections to the first hyperpolarizability of the lithium salt of pyridazine Li-H3C4N2.

In this work we report results of vibrational corrections to the polarizability and first hyperpolarizability of the lithium salt of pyridazine Li-H3C4N2 obtained at the second-order Mo̸ller-Plesset theory level with the aug-cc-pVDZ basis set. The calculations were carried out by means of the perturbation theoretical method of Bishop and Kirtman and also using a variational approach proposed here. The results obtained show that at the static limit, the pure vibrational corrections for the polarizability and first hyperpolarizability have the same order of magnitude of the corresponding electronic contributions. Comparisons between the results obtained through the two methods show that the perturbation theoretical method is not suitable to treat the system studied, while the variational methodology presented seems to be an alternative approach to treat anharmonic systems.