The semiempirical approach to electronic structure of ionic crystal surface

Two essentially different semiempirical methods (Mulliken-Ruedenberg and INDO) have been used to calculate the electronic structure of the (001) surface for some alkali halides (LiF, LiCl, NaF, NaCl) within the framework of different surface models (slab infinite in two dimensions, molecular cluster and the slab placed over the point-ion support). The computational procedure has taken into account both the bond breaking of surface atoms and the electrostatic potential difference between the surface atoms and the bulk together with the charge density redistribution obtained self-consistently. The problem of the optimum choice of the set of points in the two-dimensional Brillouin zone necessary for the calculation of the self-consistent crystal potential is discussed. The results for the electronic structure of the surfaces of alkali halides are compared with those obtained by means of surface Green functions methods.