Molecular electric polarizabilities. CI and explicitly correlated electric-field-variant functions. Calculation of the polarizability of H₂

The concept of the so-called electric-field-variant (EFV) functions (functions with explicit dependence on the external electric field strength) is applied within the CI method. A similar treatment of the electric-field perturbation is also proposed for gaussian geminals. Both methods are illustrated by calculation of the static electric dipole polarizability of H₂. With variation of a single parameter, which enters both the perturbed function and the second-order perturbed energy, accurate polarizability values can be obtained without any explicit extension of the set of functions employed for the unperturbed system.