Cusp-condition constraints and the thermodynamic properties of dense hot hydrogen

Abstract

The thermodynamic properties of liquid hydrogen are investigated at high densities and high temperatures where full molecular dissociation is expected to be attained. Nonlinear electronic response is taken into consideration by imposing rigorous cusp-condition constraints on the electron-nucleus (proton or deuteron) structure factor, and by requiring that it leads to the form of a linear-response theory in the high-density and high-temperature limits. The aim of the new structure factor is to account properly for the accumulation of the electron charge at distances from the nuclei where linear-response theory is insufficient. Using a quasi-one-component model and the Gibbs-Bogoliubov inequality with a hard-sphere reference system, it is shown that, compared with the commonly used linear methods, response with an enforced cusp condition lowers the free energy and leads to a better agreement with recent ab initio calculations in the energy and pressure of the hydrogen plasma.