Molecular hyperpolarizabilities. I. Theoretical calculations including correlation

Static polarizabilities and hyperpolarizabilities for molecules are investigated at the correlated level. The finite-field, coupled Hartree-Fock theory is used as a zeroth-order approximation, with correlation included by using the linked-diagram expansion and many-body perturbation theory, that includes single, double, and quadruple excitation diagrams. The theory is illustrated by studying the hydrogen fluoride molecule. It is demonstrated that the correlation effect for the hyperpolarizabilities $\stackrel{\ensuremath{\leftrightarrow}}{\ensuremath{\beta}}$ and $\stackrel{\ensuremath{\leftrightarrow}}{\ensuremath{\gamma}}$ can be quite large. The average polarizability and dipole moment of HF are in excellent agreement with experiment. The relative importance of the various types of diagrams contributing to electric field properties are discussed. The dependence of the computed hyperpolarizability on basis sets is also investigated.