Valence charge in a solid at 0 K viewed as a pressure-ionization effect

Modified Saha ionization theory has recently been used to obtain the dominant pressure and thermal ionization effects in the "intermediate" region (0.5-10 TPa) of the equation of state. The present work is aimed at providing the justification for the use of this theory in the presence of interactions. The valence charges at 0 K at normal density as determined using this theory are in very good agreement with their normal valence charges for a number of elements. The equation of state as computed from it is also in good agreement with the Thomas-Fermi-Dirac equation of state. Finally the theory is shown to simulate the valence transition under pressure in Eu and Yb.