Environmental effects on anion polarizability: Variation with lattice parameter and coordination number

The results of ab initio calculations of in-crystal ionic polarizabilities, a, over a wide range of lattice parameters, R, are presented for LiF, NaF, KF, LiCl, NaCl, KCl, LiBr, NaBr, KCl, and MgO. The derivatives of the mean polarizability with respect to lattice parameters are compared with experimental values obtained from the variation of the refractive index with pressure. The: environmental effects on the polarizability of an anion may be viewed as the consequence of imposition of a confining potential on its electron density whose origin includes Coulombic interactions and the exclusion of these electrons from the region occupied by the electron density of the first-neighbor shell of cations. This model suggests scaling relationships, between values of a(R) obtained at different levels of calculation and for a given anion with different cations, which are shown to be semiquantitative. These findings lead to the proposal of a universal representation of the polarizability of a given anion, which predicts the dependence on lattice parameter and crystal form and transfers from one substance to another.