Crystallization in single- and multicomponent neutron star crusts

Abstract

We use Molecular Dynamics simulations to study the formation and stability of single and multicomponent lattices in the outer crust of Neutron Stars. Including an improved treatment for Gaussian charge distributions of ions we obtain the expressions for the potential and forces arising from electron screened Coulomb interactions using the efficient Ewald sum procedure. %in the plasma. Our findings show that for baryon densities in the outer crust a point-like ion treatment can not fully describe the crystallization behaviour thus the Coulomb parameter, $\Gamma_C$, along with the usual screening parameter, $\kappa$, due to charge neutralizing electron polarizable background, must be complemented with an additional parameter, $\eta$, providing information on the finite size of ions. In our approach we find that including beyond point-like approaches in screened plasmas has a robust impact on calculated lattice energetic stability decreasing crystallization energies per baryon up to $\sim 40\%$ with respect to point-like interaction and, as a consequence, melting point resulting displaced to lower temperatures.