The effective ion-ion potential and compressibility of alkali metals

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Abstract
Using the local Heine-Abarenkov model potential, the effective ion-ion potential and interatomic force constants of alkali metals are calculated, and are compared with the results obtained using other models. The interatomic force constants so obtained are in good agreement with those derived from fitting the experimental phonon spectra and give a set of important data for the binding forces of crystals with various lattice defects. Dynamical elastic constants are also calculated using the long-wave phonon method and are also compared with results obtained using other models. The compressibility problem, proposed by Brovman and Kagan (1970), is that the two (static and dynamical) methods for calculation of the elastic constants in terms of second-order perturbation based on the same pseudopotential do not give identical results. This problem is investigated quantitatively and is shown to be important for alkali metals.