Theoretical studies of vacancies in Al and Cu

We use the real-space linear-muffin-tin-orbital approach, within the atomic-sphere approximation to calculate the electronic structure around vacancies in Al and Cu and divacancies in Al. A defect consisting of a Cd-monovacancy pair in Al is also considered. The electric-field gradient at the nucleus and the asymmetry parameter η for sites in the near neighborhood of the vacancy in these various situations were also obtained. The calculated values are in good agreement with experiment when available. Our results confirm the failure of the point-charge model when applied to obtaining the electric-field gradient at the nucleus in metallic systems and show that the defect with quadrupole frequency ${\mathrm{\omega }}_0$=64 Mrad/sec, created by low-temperature implantation of In in Al, can indeed be assigned to a Cd-monovacancy pair.