Vacancy formation volumes in simple metals

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Abstract
A comparison is made between various models for calculating the vacancy formation volume Omega ' in simple metals. It is shown to be completely inadequate to use the well known formula (e.g. Temkin 1970) Omega f= Omega + Sigma F*i.Ri/3B with interatomic forces derived from rigid pair potentials. Satisfactory results are only achieved with a theory which at least includes the density dependence of the potentials as well as the large density dependent term in the total energy (Finnis 1974). It is found to be essential to include anharmonicity in Na. Since even the density dependent model is suspect, particularly for Al, an attempt is made to go beyond it by letting the density refer to the local atomic environment.