Charge distribution in heterovalent alloys

Abstract

The selfconsistent charge density is calculated by means of the density functional formalism using a local exchange-correlation potential for a simple jellium model of a divalent impurity and a vacancy in a monovalent host. The resulting charge density around the impurity does not lend itself to an interpretation in terms of a surface dipole layer, though the dependence of the total charge transfer on the density is as predicted by the dipole model. The charge density inside a vacancy is found to be higher than that obtained by folding over a free surface; the calculated formation energy is an order of magnitude lower than typical experimental values. The validity of the Thomas-Fermi approximation for this model is discussed.