Theoretical high-pressure equations of state and phase diagrams of the alkali metals

Abstract

A two-parameter Heine-Abarenkov local pseudopotential is used to fit experimental room-temperature isotherms of lithium, sodium, and potassium up to pressures of 100 kbar. Lattice dynamics and one-component-plasma fluid variational theory are then used to compute solid-solid and solid-liquid phase boundaries, which are found to be in good agreement with experiment. The theoretical shock-compression Hugoniot curves differ significantly from experiment near 1 Mbar, and anomalously low values of the theoretical lattice Grüneisen parameter are obtained at very high compression. Further improvements in the theoretical models are suggested.