Calculation of the Cohesive Energies and Bulk Properties of the Alkali Metals

The cohesive energy and zero-pressure density of the alkali metals have been calculated using the self-consistent augmented-plane-wave method and the statistical (X) exchange-correlation approximation. For the value of which makes a single determinant of atomic spin orbitals satisfy the virial theorem, the lighter alkali metals are computed to have cohesive energies and zero-pressure densities which are too large (errors of 22 and 16% for Li) with respect to experiment. To test the sensitivity of these results to the choice of, the same calculations have been performed with set equal to 23. This choice of produced more uniformly good results for all the alkali metals with the largest errors occurring for cesium (errors of 7 and 9%, respectively). It is suggested that these results may be a consequence of the large change in the valence electronic charge density that occurs when the lighter alkali-metal atoms come together to form the solid. It is not suggested, however, that =23 be used in all energy-band calculations.