B3LYP investigation of response properties of alkali halides on external static electric fields

Structural, dielectric, and optical properties of six alkali halides were investigated by all-electron B3LYP hybrid density functional calculations. A response of their electronic and structural properties to the external static electric fields was also investigated. While the applied electric field only marginally affects the lattice parameter, the internal relaxation of ions is somewhat more pronounced with the cations displaced along with the field and anions opposite to the field. We further find that in the presence of electric field the valence and conduction bands widens resulting in the reduced band-gap. An explanation for this effect is provided, which is related to a slight delocalization of states in the presence of external electric field. However, this effect is far too small to account for the dielectric breakdown of alkali halides. For this reason, the dielectric breakdown was considered on the basis of von Hippel’s low-energy criterion and Callen’s equation, for which the calculated dielectric constants and optic transverse mode frequency were used. The obtained dielectric strengths are in fair agreement with experiment.