Positron annihilation and positron electron correlation effects in high-T-c oxides

We have calculated electron and positron states in the Nd2-xCexCuO4 compound, for the perfect bulk lattice as well as when vacancy defects are included. We study the sensitivity of the results to different approximations in the positron potential. We also compute the annihilation rate and the electron-positron momentum density using the local density approximation and the newly developed gradient correction for the electron-positron contact term. Our main goal is to give predictions for the Fermi surface signals.