Positrons around vacancies in Al

Some physical quantities have been calculated concerned with the state of a positron trapped at an aluminium vacancy. Electron density distributions around the vacancy were taken from the results of the model calculations which have been recently performed by the author. The method of the analysis is based on the positron potential proposed by Stott et al. (Phys. Rev.; B11:1 (1975)) but in order to simplify the calculations some rough approximations were adopted. Nevertheless the preliminary calculations are reliable enough to give some semi-quantitative conclusions from a viewpoint differing from a jellium model. The calculated positron-vacancy binding energy was 0.8 eV and the positron wavefunction extended to practically 8 A from the vacancy centre. The numerical result for the lifetime of the trapped positron showed 273 ps neglecting the effect of the annihilation with core electrons and this value is in tolerably good agreement with the experimental value (240 to 250 ps) considering the approximations made in this letter. (author)