Direct MD simulation of liquid-solid phase equilibria for three-component plasma

摘要

The neutron rich isotope 22Ne may be a significant impurity in carbon andoxygen white dwarfs and could impact how the stars freeze. We perform moleculardynamics simulations to determine the influence of 22Ne in carbon-oxygen-neonsystems on liquid-solid phase equilibria. Both liquid and solid phases arepresent simultaneously in our simulation volumes. We identify liquid, solid,and interface regions in our simulations using a bond angle metric. In generalwe find good agreement for the composition of liquid and solid phases betweenour MD simulations and the semi analytic model of Medin and Cumming. The tracepresence of a third component, neon, does not appear to strongly impact thechemical separation found previously for two component carbon and oxygensystems. This suggests that small amounts of 22Ne may not qualitatively changehow the material in white dwarf stars freezes. However, we do findsystematically lower melting temperatures (higher Gamma) in our MD simulationscompared to the semi analytic model. This difference seems to grow withimpurity parameter Q_imp and suggests a problem with simple corrections to thelinear mixing rule for the free energy of multicomponent solid mixtures that isused in the semi analytic model.