Extended Model of Bond Charges and Its Application in Calculation of Optical Properties of Crystals with Different Types of Chemical Bonds

Abstract

AbstractA method for calculating the optical characteristics of crystals with different types of chemical bonds within the framework of the dielectric theory of chemical bond put forward by Philips and Van Vechten is suggested. The calculating scheme which does not contain adjustable parameters is based on the bond charge model designed by Levine, which is generalized for the case of multiple bonds and modified involving the density functional method data on the spatial distribution of electrons in atoms. The structural elements of the method are: the screened Coulomb potentials and radii of the atomic core, bond lengths and charges, and the distances from the nuclei to the centres of gravity of the latter. The calculated characteristics of the crystals (dielectric permittivity, quadratic and cubic non‐linear susceptibilities, electrooptical constants) are in good accordance with experimental findings. An attempt is made to predict the non‐linear optical characteristics according to precision X‐ray diffraction data on the electron structure of its only representative, lithium formate deuterate LiHCO2 · D2O, whereby a fairly good fit with the experimental data is achieved.