On the reliability of various theories for a description of electron-positron densities in metals

Full text: For a proper theoretical description of the annihilation of positrons in metals, it is necessary to calculate the electron-positron (e-p) momentum density in these systems including correlation effects due to the Coulombic attraction between the annihilating particles. In this contribution, we use various theoretical approaches for such calculations, and we compare the results with corresponding experimental data of (e-p) momentum densities in metallic magnesium, copper, cadmium, and yttrium. It is shown that the Bloch-modified ladder (BML) theory is - in contrast to other approaches proposed in the literature - able to achieve a satisfying agreement between theory and experiment for all metals investigated. Refs. 3 (author)