Calculation of Energy Bands in Alkali Halides

Abstract

The electronic energy bands in LiF, NaCl, and KBr have been calculated using the augmented-plane-wave (APW) method. The usual APW method is improved upon by including nonspherical terms in the potential and by varying the Slater free-electron-exchange approximation in order to match experimental band-gap data. It was found that the nonspherical terms have about an 0.8-eV effect in LiF, a 0.4-eV effect in NaCl, and a 0.1-eV effect in KBr. It was found that if the exchange potential is increased by about 10%, experimental band-gap data can be matched. Transitions calculated from the energy-band calculations were compared with experimental optical-absorption and optical-reflectance data. Agreement is generally good. Using numerical differentiation, the effective mass at the bottom of the conduction band was calculated. The effective masses were found to be approximately $1.2m_e$ for LiF, $0.6m_e$ for NaCl, and $0.5m_e$ for KBr. Experimental values exist only for KBr and are in good agreement.