Correlation effects for positron annihilation with core and semicore electrons

We present a theory for calculating the momentum distribution of annihilating electron-positron pairs in solids. The theory leads to a scheme in which the momentum density within the independent particle model for a given electron state is weighted by the annihilation rate of that state. The annihilation rate is calculated within the generalized gradient approximation. The scheme describes the suppression of the electron-positron correlations due to the charge inhomogeneity and explains the trends observed for positron annihilation with core and semicore electrons.