“Non-muffin tin” corrections of the SCF X_α-SW Method. I

The recently developed crystalline cluster method within the framework of the Johnson multiple scattering technique was successfully used in calculations of ionic cubic crystals and the defects with a cubic symmetry. In this paper a simple way of extension of the method to noncubic systems by a partial elimination of “muffin-tin” approximation (MTA) is proposed.

The procedure suggested does reduce the intermediate integrals to the one-dimensional ones, and they are calculated analytically. It is supposed that an approach of taking into account the nonspherical shape of the potential inside the “muffin-tin” (MT) spheres will be effective in crystals with an ionic type of chemical bond.