Direct linear term in the equation of state of plasmas

We discuss a long-standing discrepancy in the equation of state of charge-neutral plasmas, the occurrence of an $e^2$ direct term. This $e^2$ term may appear in dependence of the way to determine the mean value of the potential energy. We show that such a contribution should not appear for pure Coulomb interaction.

Figure 1

Function $Q\left(\xi \right)$ according to Eq. (3) and $Q_1\left(\xi \right)=Q\left(\xi \right)-\xi /6$.