J. Phys. III France
Volume 2, Numéro 6, June 1992
Page(s) 905 - 913
DOI: 10.1051/jp3:1992168
J. Phys. III France 2 (1992) 905-913

On the pressure dependence of the vacancy formation energy for the alkalis

L. F. Magaña

Instituto de Física, Universidad Nacional Autónoma de México, Apartado Postal 20-364, Código Postal 01000, México D.F. México

(Received 5 December 1991, accepted 17 February 1992)

We express the vacancy formation energy for the alkalis, $E^{\rm f}$, as : $E^{\rm f} = \Delta E_{\rm eigen} - g (r_{\rm s})$, where $\Delta E_{\rm eigen}$ is the change in the energy eigenvalues of the electrons, when the vacancy is formed, which is calculated in a fully self consistent way using density functional formalism, for a set of six different values of $r_{\rm s}$ for each material and $g (r_{\rm s})$ is a function of the density parameter $r_{\rm s}$ which is used to take into account other contributions to $E^{\rm f}$ (it is fitted to the experimental results of $E^{\rm f}$ using the set of corresponding values of $\Delta E_{\rm eigen}$ at atmospheric pressure). Having $\Delta E_{\rm eigen}$ as function of $r_{\rm s}$ and $g (r_{\rm s})$, we have $E^{\rm f}$ as function of $r_{\rm s}$ for every one of the five alkalis. We found that the vacancy formation energy decreases when $r_{\rm s}$ decreases, for Li and Na. It increases for Rb and it is practically constant for K and Cs.

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