Electron-positron correlations in silicon

A number of approaches to treat the electron-positron correlation effects i s used to study electron-positron momentum densities and positron annihilat ion rates in bulk silicon. Also, the nonlocal effects are explicitly taken into account within the weighted density approximation (WDA), giving rise t o nonlocal state-selective electron-positron correlation functions. The WDA results for the electron-positron momentum densities and annihilation rate s are compared to the experimental data and to calculations performed withi n the independent-particle model and local-density approximation. Additiona lly, the generalized-gradient approximation is used to calculate nonlocal, but state independent, quantities. The importance of nonlocality and state- dependence of the electron-positron correlation functions, and the role of the positron wave function, are discussed in detail.