Ab initiocalculations of the physical properties of ionic crystals

First-principles calculations of the physical properties of ionic crystals are reviewed. Two markedly different approaches within the framework of the density functional theory are described. In one of them, the electron spectrum and wave functions are treated within the standard band picture based on the solution of Kohn–Sham equations. In the second approach, the total electron density of a crystal is represented as a superposition of the densities of individual ions. The problem of determining the electric polarization of a crystal is discussed for each approach. It is shown that it is the use of Bloch functions rather than the physics of the phenomenon that complicates the solution of this problem within the Kohn–Sham framework. The deformable and polarizable ion model is described in detail, and its application to calculating many properties of ionic crystals, including the lattice dynamics and structural stability of crystal phases, is discussed.