One--Component Plasma Equation of State Revisited via Angular--Averaged Ewald Potential

Abstract: We present analytic fits of classical one--component plasma (OCP) internal energy over a wide range of coupling parameter $0.01\le\Gamma\le 170$ using Monte--Carlo data in the thermodynamic limit. We extend the dataset obtained in [Demyanov and Levashov, Phys. Rev. E 106, 015204 (2022)] using the angular--averaged Ewald potential with additional points at strong coupling ($\Gamma=120,\ 150,\ 170$). We then fit two frequently used functional forms for the OCP equation of state: (i) a five-parameter equation by Caillol [J. Chem. Phys. 111, 6538--6547 (1999)] and (ii) the equation by Potekhin and Chabrier [Phys. Rev. E 62, 8554 (2000)] that enforces the Debye--H\"uckel limit. The presented fits reproduce our MC data within statistical uncertainties, recovering the correct weak-coupling behavior. Coefficients, recommended validity ranges, and comparisons to prior analytical and simulation results are provided.