Positron States in Materials: Dft and QMC Studies

Abstract

First-principles approaches based on density functional theory (DFT) for calculating positron states and annihilation characteristics in condensed matter are presented. The treatment of electron-positron correlation effects is shown to play a crucial role when calculating affinities and annihilation rates. A generalized gradient approximation (GGA) takes the strong inhomogeneities of the electron density into account and is particularly successful in describing positron characteristics in various materials such as metals, semiconductors, cuprate superconductors and molecular crystals. The purpose of Quantum Monte Carlo (QMC) simulations is to provide highly accurate benchmark results for positron-electron systems. In particular, a very efficient QMC technique, based on the Stochastic Gradient Approximation (SGA), can been used to calculate electron-positron correlation energies.