Nonlocal effects in the electron-positron interaction in metals

Abstract

We study the importance of the nonlocal electron-positron interaction for positron annihilation characteristics in simple and transition metals. This is accomplished by using the weighted density approximation, giving rise to nonlocal and energy-dependent electron-positron correlation functions. We apply this formalism to study the momentum-dependent and momentum-averaged electron-positron enhancements of the positron annihilation rates and the three-dimensional electron-positron momentum densities. The results of the present approach are compared to those obtained within the local density approximation, generalized gradient approximation, Bloch modified ladder approximation, and experimental data. We find that while nonlocality of the electron-positron correlations is of substantial importance for the core and d electrons in transition metals, for nearly-free-electron bands the energy dependence of the electron-positron correlation functions is of more significance.