Structure of cold nuclear matter at subnuclear densities by quantum molecular dynamics

Structure of cold nuclear matter at subnuclear densities for the proton fraction x = 0.5, 0.3, and 0.1 is investigated by quantum molecular dynamics (QMD) simulations. We demonstrate that the phases with slab-like and rodlike nuclei, etc. can be formed dynamically from hot uniform nuclear matter without any assumptions on nuclear shape, and also systematically analyze the structure of cold matter using two-point correlation functions and Minkowski functionals. In our simulations, we also observe intermediate phases, which have complicated nuclear shapes. It has been found out that these phases can be characterized as those with negative Euler characteristic. Our result implies the existence of these kinds of phases in addition to the simple "pasta" phases in neutron star crusts and supernova inner cores. In addition, we investigate the properties of the effective QMD interaction used in the present work to examine the validity of our results. The resultant energy per nucleon ε _n of the pure neutron matter, the proton chemical μ _p⁽⁰⁾ in pure neutron matter and the nuclear surface tension E_surf are generally reasonable in comparison with other nuclear interactions.