In-crystal hyperpolarizabilities ofF−andCl−

Ab initio hyperpolarizabilities $\gamma$ and $B$ are calculated at the self-consistent field level for the ions ${\mathrm{F}}^{-}$ and ${\mathrm{Cl}}^{-}$ in lithium halide crystals. Large reductions with respect to free-ion values are found, and the physical factors contributing to the reduction are discussed. Artifacts arise for a pointcharge model of the crystal but are removed when a more realistic model of the ionic environment is used. The final calculated values are in good agreement with the limited experimental data available from third-harmonic generation and three-wave-mixing experiments.