ENERGETICS OF VACANCY AND SUBSTITUTION IMPURITIES IN ALUMINUM BULK AND CLUSTERS

We present a careful study of the energetics of vacancy and substituti onal impurities in aluminum in both the bulk and small cluster environ ments. The calculations are done within the framework of the local-den sity-functional formalism and are based on the pseudopotential method with plane-wave expansion and periodic boundary conditions. Both the i onic and electronic degrees of freedom are fully relaxed. The electron ic structure problem is treated with a preconditioned conjugate-gradie nt method that applies equally well to insulators and metals, and is s uitable for parallel computing. We have considered up to 216 atoms in the supercell, and we show that reliable results can be obtained with 108-atom cells with proper k-point sampling. Vacancy-formation energy, heats of solution of the impurities and the relaxations near the defe cts air in good agreement with available experimental data. The energe tics of substitution in small clusters was found to be rather differen t from bulk.