title: Comment on "Direct linear term in the equation of state of plasmas".
abstract: In a recent paper [Phys. Rev. E 91, 013108 (2015)], Kraeft et al. criticize known exact results on the equation of state of quantum plasmas, which have been obtained independently by several authors. They argue about a difference in the definition of the direct two-body function Q(x), which appears in virial expansions of thermodynamical quantities, but Q(x) is not a measurable quantity in itself. Differences in definitions of intermediate quantities are irrelevant, and only differences in physical quantities are meaningful. Beyond Kraeft et al.'s broad statement that there is no agreement at order ρ(5/2) in the virial equation for the pressure, we show that their published results for this quantity are in fact in perfect agreement with previous existing expressions.
authors.affiliation: Laboratoire de Physique, ENS Lyon, UMR CNRS 5672, 46 allée d'Italie, 69364 Lyon Cedex 07, France.
authors.forename: A
authors.initials: A
authors.lastname: Alastuey
authors.affiliation: Institut UTINAM, Université de Bourgogne-Franche-Comté, UMR CNRS 6213, 16 route de Gray, 25030 Besançon Cedex, France.
authors.forename: V
authors.initials: V
authors.lastname: Ballenegger
authors.affiliation: Institut für Physik, Humboldt Universität Berlin, Newtonstrasse 15, 12489 Berlin, Germany.
authors.forename: W
authors.initials: W
authors.lastname: Ebeling