Equation of State for warm Neutron Star outer crusts

Abstract

We describe the equation of state (EoS) of a warm ion plasma as obtained by performing microscopic many-body simulations using Molecular Dynamics computational techniques. Using the cold one-component plasma (OCP) composition in the Neutron Star (NS) outer crust assumed in Murarka et al. (2022) with a representative heavy nucleus for each density, we refine previous calculations. We include electron screening and modeling of ions as finite-size Gaussian distributions in the interaction potential, together with an efficient Ewald energy summation procedure. From this, the EoS relation $P(n_B,T)$ is obtained as a function of baryonic density and temperature in the NS outer crust under conditions $n_B\in[7.48\times 10^{-10},2.09\times10^{-4}]$ $ \rm fm^{-3}$ , $k_{B}T\in[1,5]$ MeV. In order to improve the usability of our results we provide tabulated data values along with a neural network parametrization available in the Zenodo repository, see https://zenodo.org/records/15348712. We find that even at moderate temperatures, thermal effects of ions are key in the higher density region closer to the inner crust, when described using a thermal effective parametrization based on the thermal adiabatic index $\Gamma_{th}$. We compare our results with other EoS in the literature performing a critical discussion.