Defect spectroscopy with positrons: a general calculational method

Abstract

A new, versatile method of calculating positron states in solids is described. The main purpose is to develop a practical scheme accurate enough to reliably predict annihilation characteristics for positrons trapped at defect clusters of varying size, geometry and impurity environment, in order to help analyse experimental data. The positron potential is constructed from the full lattice electrostatic potential, and a local-density approximation for the correlation potential. The three-dimensional positron Schrodinger equation is solved by finite-element techniques. Enhancement effects in the annihilation rate are parametrised in a simple way, both for simple and transition metals. The applications discussed include vacancies, vacancy clusters and impurity-vacancy complexes in a number of metals. Good agreement with experiment in cases where comparison is possible suggests a good predictive power for the scheme.