Strongly screened Yukawa fluids: Benchmark thermodynamics and the soft-to-hard interaction crossover

The excess energy and pressure of a strongly screened Yukawa fluid (screening parameter κ in the range of 5 ≤ κ ≤ 12) are calculated using molecular dynamics (MD) simulations. These results are used to verify the accuracy of the variational approach that uses a fluid of hard spheres as a reference system, and the relatively high precision of this method is documented. We also show that the energy and pressure cannot be described by the ion-sphere model, which works well under weak screening. The Rosenfeld–Tarazona scaling for the thermal component of excess energy remains applicable, but in a slightly modified form compared with that in the weak-screening regime. The effective inverse-power-law exponent is determined. The excess entropy is evaluated using the variational approach and the MD excess energy data, and a good agreement is demonstrated. These results can be of some interest in the context of complex plasmas and colloidal suspensions as well as for systems in the vicinity of the soft-to-hard interaction crossover in general.