Comment on ‘‘Equation of state and phase diagrams for dense multi-ionic mixture plasmas’’

An equation of state for dense fluid binary-ionic mixture (BIM) plasmas was derived recently by Ogata, Iyetomi, Ichimaru, and Van Horn [Phys. Rev. E 48, 1344 (1993)] from extensive Monte Carlo simulations data. They emphasized in particular the significance of finding negative deviation from the linear-mixing approximation. In this Comment, I show that the important features of their results are the outcome of their particular choice for the equation of state of the one-component plasma, which has relatively large error bars that have not been properly taken into account and are not necessarily borne out by their data for the binary mixtures. I repeated their analysis of their same data for the bindary mixtures, but used another, comparable, one-component plasma fluid equation of state to find always positive deviations from linear mixing, in contradiction also with the sum-rule analysis of their free energy with respect to the zero separation of the screening potentials.