Hyperpolarizabilities of Some Polar Diatomic Molecules

The energy E of a polar diatomic molecule in a uniform external electric field F is expressible as $${\mathrm{E=E}}_0{\mathrm{-p}}_i{F}_i{\text{−(2 !)}}^{\text{−1}}{\alpha }_{\mathrm{ij}}{F}_i{F}_j{\text{−(3 !)}}^{\text{−1}}{\beta }_{\mathrm{ijk}}{F}_i{F}_j{F}_k\mathrm{-···,}$$ where E₀ is the energy of the molecule out of the field, p_i is the permanent dipole moment, α_ij is the dipole polarizability tensor, and β_ijk is the first hyperpolarizability tensor. In this work, theoretical results are presented for α_ij and β_ijk for some diatomic molecules. The zero‐order wavefunctions used in these calculations are extended basis Hartree—Fock functions of the Roothaan type. The values of α_ij and β_ijk are obtained via an uncoupled Hartree—Fock scheme. The results for α_ij are compared with previous uncoupled and coupled self‐consistent‐field calculations. The present scheme improves upon the previous uncoupled calculations and compares favorably with the results obtained in self‐consistent‐field calculations. Finally, these polarizabilites and hyperpolarizabilites are found to be quite sensitive to the quality of the zero‐order wavefunctions.