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 ap proximation electron-positron enhancement factors far the core electrons ar e 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 charge density are studi ed. The formalism is applied to ab initio calculations of positron lifetime s in a variety of metals and silicon. The influence of various approximatio ns to the electron-positron interaction on the positron lifetimes is also p resented. The weighted density approximation results are compared to those calculated within the local density approximation, the recent generalized g radient approximation and with experimental data.