Polarizability of the Iodide Ion in Crystal

Abstract

The electronic dipole polarizability of the iodide ion in solid cubic NaI and KI is derived from ab initio electronic structure computations as function of closest cation−anion separation for the four-coordinated zinc blende structure, the 6-fold coordinated rock salt structure, and the 8-fold coordinated phase having the CsCl structure. The contributions from electron correlation were computed using Moller−Plessett perturbation theory taken to the second order. For both NaI and KI, the anion polarizability predicted for the observed rock-salt polymorph at the equilibrium separation agrees well with the value deduced from experiment. The anion polarizabilities increase with both decreasing coordination number at constant distance and with increasing distance at constant coordination number. Both the polarizabilities and their contributions from electron correlation are suppressed in-crystal relative to those computed for the free iodide ion. The ab initio predictions for the derivatives of the anion polar...