Model calculations for H⁻impurity centres in alkali halides

An existing consistent set of model potentials for alkali halides formulated for convenient use in defect applications is extended to incorporate hydrides. The additional parameters required are fitted to the limited available experimental data for perfect alkali hydride crystals. Calculations of local-mode frequencies for isolated H - substitutional (U-centre) and interstitial impurities, H - H - , H - D - , H - -cation-impurity and H - -anion-impurity pairs in alkali halides are reported. These calculations, which are based on large periodic defect cells, involve no further adjustment parameters and are in good agreement with results of infrared absorption measurements found in the literature.