The effect of the positron distribution and electron-positron correlations on the electron-positron momentum density for SiC

To interpret the data on positron annihilation in solids in terms of the electron momentum density, both the electron-positron interaction and the positron distribution have to be considered explicitly. In this work we discuss the influence of the shape of the positron wavefunction and electron-positron (e-p) correlations on the calculated e-p momentum density and lifetime of the positron in perfect SiC. It is shown that the form of the positron distribution in the Wigner-Seitz cell has a considerable effect on the calculated annihilation characteristics. The results obtained within the independent particle model are compared with their counterparts incorporating e-p correlation functions locally and beyond the local density approximation. The calculations have been performed for SiC of 3C cubic (zinc-blende) structure within the linear muffin-tin orbital atomic sphere approximation method.