Pseudopotential study of alkali metals: Unified approach

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Abstract
A comprehensive unified calculation of both the lattice static and dynamical properties for the whole alkali-metal group (except Cs) in the pseudopotential framework is presented. Both Ashcroft and Heine-Abarenkov pseudopotentials combined with different forms of static dielectric functions have been used to calculate cohesive energy, equilibrium lattice parameters, second-order elastic constants, pressure derivatives of second-order elastic constants, and phonon dispersion in the symmetry directions for the four alkali metals Li, Na, K, and Rb. The mode Grüneisen parameters have been calculated for Na and K, for which experimental data are available. It is found that the two-parameter Heine-Abarenkov potential in conjunction with a dielectric function of a very simple form proposed recently by Taylor yields satisfactory results. The Heine-Abarenkov potential, coupled with the self-consistent dielectric function of Vashishta and Singwi, gives similar results. This agreement is justified from a comparison of the correction factor introduced by the two dielectric functions, over the screening function of Lindhard.