Effects of inner-core 2p states on melting curve and structure of dense sodium at high pressures

We have carried out ab initio molecular-dynamics (MD) simulations of dense liquid/solid sodium for 3s(-) and 2p3s-valence-electron models, and for different valence electron-ion interactions at high pressures. We have found that the melting curve has a melting point maximum, which depends on the type of valence-electron models used at high pressures. We have shown that, if we consider inner-core 2p states, the repulsive interatomic force becomes stronger and the pressure and temperature of the maximum melting point increase. We have investigated the effect of inner-core 2p states on the structure of liquid sodium, and found that, though the differences in the structures obtained with different valence-electron models are negligible in a relatively low-pressure region, the differences are significant at extremely high pressures, since inner-core 2p states play important roles at high pressures. We have also shown that the ultrasoft pseudopotential method and projector augmented-wave method give almost the same results.