ABINITIO CALCULATION OF POSITRON-ANNIHILATION RATES IN SOLIDS

Recently, Jensen showed that the positron annihilation rates in metals can be calculated rather successfully within the local-density approximation (LDA) using the total electron density as the only input. Thus, the division into core, valence, and, in the case of transition metals, the d electrons, is not necessary. Jensen calculated the positron lifetimes on the basis of non-self-consistent electron structures. We have calculated in this work positron annihilation rates using self-consistent electron structures. The use of self-consistent electron densities makes the LDA lifetimes longer and, especially in the case of simple metals, a better agreement with experimental results is obtained. In this article we present results for several simple and transition metals and study the trends along the different columns and rows of the Periodic Table. Moreover, we have calculated the positron annihilation rates also for semiconductors using a slightly different enhancement function. The reasons for the success of the LDA are discussed and the implications to the calculation of lifetimes for positrons trapped at crystal defects are demonstrated by examples.