Theoretical calculation for the equations of state and phase transitions of sodium and potassium hydrides

The ionic overlap-compression model is used to calculate the equations of state, as well as the equilibrium properties, of sodium and potassium hydrides (NaH and KH). The present results agree with the experimental ones well. The NaC1-to-CsC1 phase transition pressures for both crystals are also determined. The agreement of the theoretical pressures (23.0 GPa for NaH and 4.9 GPa for KH) with the experimental measurements (29.3 GPa and 4 GPa) is rather good. The calculation shows that the effect of the zero-point vibration to the equilibrium properties and the transition pressures should not be ignored.