On the Theoretical Determination of Molecular First Hyperpolarizability

Coupled Hartree–Fock perturbation theory has been applied to evaluate the first hyperpolarizability in the molecules H2O, NH3, CH4, and CO. A group-theoretical approach has been employed, which makes it possible for a reduced file of symmetry distinct two-electron integrals to be processed at each iteration with reduced computer efforts. Several very large basis sets, including up to 4f functions on the heavy atom and 3d on hydrogen, have been retained, which yield SCF energies, dipole moments, polarizabilities, and first hyperpolarizabilities very near to the corresponding HF quantities. Except in the case of CO, large discrepancies with respect to experimental data have been found.