Non-local electron-positron enhancement factors in solids

Non-local electron-positron correlation effects in solids are studied. The weighted density approximation is applied to calculations of the non-local electron-positron correlation functions. The calculated weighted density approximation electron-positron enhancement factors for the core electrons are compared with those obtained within the local density approximation. Also differences in the electron-positron enhancement factors due to the s, p, d and f angular momentum channels of the electron change density are studied. The formalism is applied to 'ab initio' calculations of positron lifetimes in a variety of metals and silicon. The influence of various approximations to the electron-positron interaction on the positrons lifetimes is also presented. The weighted density approximation are compared to those calculated within the local density approximation, the recent generalized gradient approximation and with experimental data. (author)