Ab initio calculations of the second dynamic hyperpolarizability of LiH bymeans of Floquet theory approach

Floquet theory is used to describe the response of a molecule to applied ra diation electric field. The method of ab initio calculation of frequency de pendent (hyper)polarizabilities based on combination of perturbation theory with the finite field method has been developed. Electron correlation is t aken into account by means of the CIPSI algorithm. The total wave function expansion involves spectral, pseudospectral states and polynomial terms. Th e developed approach is applied to the calculation of the second hyperpolar izability of the lithium hydride molecule subjected to the superposition of harmonic and static electric fields. The method can be used to calculate t he higher order nonlinear properties of molecules.