Equation of state of dense plasmas by ab initio simulations: Bridging the gap between quantum molecular dynamics and orbital-free molecular dynamics at high temperature

The applicability of quantum molecular dynamics to the calculation of the equation of state of a dense plasma is limited at high temperature by computational cost. Orbital-free molecular dynamics, based on the Thomas-Fermi semiclassical approximation and possibly on a gradient correction, is the only simulation method currently available at high temperature. We show in the case of a dense boron plasma that the two approaches give pressures differing by a few percent even at temperatures as high as a few tens of electron-volts. We indicate how the pressures obtained by orbital-free molecular dynamics can be corrected in order to appear as a limit of the quantum molecular dynamics results as temperature increases. We thus obtain a method to calculate the equation of state of a dense plasma up to high temperatures where quantum molecular dynamics cannot be directly implemented.