Calculation of the momentum distributions of positron annihilation radiation in Ge

Abstract

One- and two-dimensional momentum distributions of positron annihilation radiation in Ge are calculated using the independent-particle model (IPM), the local density approximation (LDA) and the generalized gradient approximation (GGA). It is found that these three approximations are all capable of reproducing the main structures of the momentum distributions observed in the one- and two-dimensional angular correlation of positron annihilation radiation measurements. The positron annihilation rate is, however, found to be overestimated in the LDA in the low-momentum regime. While the GGA alone gives the correct total annihilation rate, it is found that the GGA is essentially just scaled with the LDA, and introduces no new momentum dependence to eliminate the overestimation of the LDA in the low-momentum regime.