CALCULATION OF VACANCY FORMATION ENERGIES IN THE ALKALI-METALS LI, NA AND K

The formation energies of vacancies in Li, Na and K have been calculated as functions of temperature using pair potentials determined from first principles. Included in the calculation is a term describing the change in entropy upon formation of the defect. This term is of critical importance in obtaining the right temperature dependence. When combined with earlier calculations of migration energies, the results agree very precisely with the measured self-diffusion energies, giving strong support to the single-defect mechanism for diffusion. On the other hand the calculated formation energies do not agree particularly well with the published measurements, leading to the suggestion that a re-interpretation of these experimental results would be useful.