Pressure dependence of positron annihilation in boron phosphide

Abstract

We have obtained the valence electron and positron charge densities in boron phosphide from wavefunctions derived in a model pseudopotential band structure calculation. The charge densities are calculated at pressures ranging from 0 to 90 GPa. We find that the positron density is maximum in the open interstices and is excluded not only from the ion cores, but also to a considerable degree from the valence bonds. Electron momentum densities are calculated in the (001–110) plane. The observation that the total positron annihilation rate increases with pressure has been explained in terms of increased positron penetration into the ion cores.