Fluid variational theory for pressure dissociation in dense hydrogen: Multicomponent reference system and nonadditivity effects

In a recent paper, standard hard-sphere variational theory has been applied to pressure dissociation in dense fluid hydrogen (Juranek and Redmer, J. Chem. Phys. 112, 3780 (2000)). The correlation contributions to the dissociation equilibrium were determined from the free energy functional using effective pair potentials and minimization with respect to the hard-sphere reference system. For simplicity, the Berthelot mixing rule was used to determine the H–H2 pair potential (which entails additive effective hard spheres), and single-component reference pair correlation functions were employed for evaluating the correlation integrals. In this paper, we employ multicomponent reference pair correlations, and we study the sensitivity of the results with respect to nonadditivity of the effective hard spheres. We compare our results with available ab initio simulation data.