Quantum‐chemical calculations of electronic and hole centres and surface of NaCl crystals (I)

A new parametrization scheme for electronic structure calculations of defects in alkali halides by the CNDO semiempirical method is presented and developed. The model of a molecular cluster is used taking into account, for the first time, the non‐point nature of ions outside the cluster, which considerably reduces the surface effect. The derived parameters reflect the ionic nature of the NaCl crystal. An attempt to calculate the F centre properties (first of all the position of its ground state level within the gap and the spin density on the neighbouring ions) indicates the necessity to extend the valence basis set by introducing an additional wave function centered at the vacancy. The parameters of the latter are derived.