Screened Interionic Potential of the Simple Metals

The modified interionic potential which includes both a direct ion-ion interaction and an indirect ion-electron-ion interaction has been studied for twelve simple metals, using Ashcroft's analytic bare-ion pseudopotential form factor and a modified Hartree dielectric function. The direct Coulomb interaction between any pair of ions is demonstrated to be exactly cancelled at distances greater than 2rc, which is around half the nearest-neighbor separation. Therefore, the interionic potential needed for a study of various properties of solids is entirely of a screened nature and has the usual Friedel oscillation in the asymptotic region. In general, however, the simple Friedel form is not a good representation for distances less than the fourth-neighbor separation. The interatomic force constants and the elastic constants derived from the screened interionic potential agreed reasonably well with experiments.