Total Energy Calculations of Alloys: Locally Self-Consistent Green’s Function Method

Abstract

There is a growing interest in first-principles investigations of materials with broken translational symmetry, for example, impurities, interfaces, and alloys. In particular, the total energy and the electronic structure calculations of systems with an arbitrary distribution of atoms on an underlying lattice will give information essential to understanding their stability and properties. At the same time two schemes most frequently used in ab initio total energy calculations for completely random alloys, the ConnollyWilliams (CW) method¹ and the methods based on the single-site approximation, as the coherent potential approximation (CPA)², have limited applicability and reliability³. Another way of approaching the solution to the electronic structure problem for disordered systems is given by the supercell technique. In this case the three-dimensional periodicity is restored although its effect on the final result can be neglected. Then conventional band structure methods can be used. However, this approach has both fundamental and technical limitations. For instance, from the basic point of view all details connected with the smearing of the electronic spectrum and the Fermi surface in alloys are lost. From the technical point of view the computational effort increases as N ³ with increasing number of atoms N in the supercell.