Contribution of Surface Distortion to the Surface Energy of Alkali Halide Crystals

The distortion of the {100} face of the NaCl-type lattice and its influence on the surface energy have been considered using a model in which the ions of the first crystal layer are allowed to displace separately and to polarize. van der Waals terms have been included in the potential function in order to make the treatment consistent with existing classical calculations on the surface energy of the undistorted surface. The configurations of lowest energy and the corresponding surface energy corrections have been computed for all NaCl-type alkali halides except LiF, for which compound no stable minimum could be found. A short discussion on the approximational aspects of the calculations is given.