Direct molecular dynamics simulation of liquid-solid phase equilibria for a three-component plasma

摘要

The neutron-rich isotope 22Ne may be a significant impurity in carbon and oxygen white dwarfs and couldnimpact how the stars freeze. We perform molecular dynamics simulations to determine the influence of 22Nenin carbon-oxygen-neon systems on liquid-solid phase equilibria. Both liquid and solid phases are presentnsimultaneously in our simulation volumes.We identify liquid, solid, and interface regions in our simulations usingna bond anglemetric. In generalwe find good agreement for the composition of liquid and solid phases between ournMD simulations and the semianalytic model of Medin and Cumming. The trace presence of a third component,nneon, does not appear to strongly impact the chemical separation found previously for two-component carbonnand oxygen systems. This suggests that small amounts of 22Ne may not qualitatively change how the material innwhite dwarf stars freezes. However, we do find systematically lower melting temperatures (higher u0002) in our MDnsimulations compared to the semianalytic model. This difference seems to grow with impurity parameter Qimpnand suggests a problem with simple corrections to the linear mixing rule for the free energy of multicomponentnsolid mixtures that is used in the semianalytic model.