Abstract
A rigid shift of a single muffin-tin potential does not generally satisfy the Friedel sum rule. An additional scattering potential of a simple form, which basically comes from the screening effect is taken into account so that the whole scattering effect satisfies the Friedel sum rule. Some problems of the rigid-muffin-tin approximation and the modifications arising from the present method are discussed with some example calculations for Al, Cu, Nb and Mo.