POSITRON STATES IN VACANCIES AND VOIDS

We have calculated the positron wavefunctions and annihilation rates in voids in aluminium as functions of void radius using density functional theory with the non-local approximation to the positron-electron correlation potential developed by Jensen and Walker. Our calculations show the gradual evolution of the positron state, as the radius increases, from a state extending over the whole of the defect volume in monovacancies to a state localized at the void surface in large voids. We find that for voids with radii larger than about 5 angstrom the lifetime is independent of void size.