Theoretical studies of Positron annihilation in Lead chalcogenides PbX

The independent particle model (IPM) coupled with the empirical pseudopotential method (EPM) was used to compute the thermalized positron charge densities in a specific family of binary tetrahedrally coordinated crystals of formula A^NB^8-N. Initial results show a clear asymmetrical positron charge distribution relative to the bond center. It is observed that the positron density is maximal in the open interstices and is excluded not only from the ion cores but also to a considerable degree from the valence bonds. Electron-positron momentum densities are calculated for the (001,110) planes. The results are used to analyze the positron effects in PbTe and PbSe. Our computational technique provides a theoretical means for interpreting the k-space densities obtained experimentally using the two-dimensional angular correlation of annihilation radiation (2D-ACAR).