Direct molecular dynamics simulation of liquid-solid phase equilibria for two-component plasmas

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Date
2012
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American Physical Society
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We determine the liquid-solid phase diagram for carbon-oxygen and oxygen-selenium plasma mixtures using two-phase molecular dynamics simulations. We identify liquid, solid, and interface regions using a bond angle metric. To study finite-size effects, we perform 27 648- and 55 296-ion simulations. To help monitor nonequilibrium effects, we calculate diffusion constants ${D}_{i}$. For the carbon-oxygen system we find that ${D}_{\text{O}}$ for oxygen ions in the solid is much smaller than ${D}_{\text{C}}$ for carbon ions and that both diffusion constants are 80 or more times smaller than diffusion constants in the liquid phase. There is excellent agreement between our carbon-oxygen phase diagram and that predicted by Medin and Cumming. This suggests that errors from finite-size and nonequilibrium effects are small and that the carbon-oxygen phase diagram is now accurately known. The oxygen-selenium system is a simple two-component model for more complex rapid proton capture nucleosynthesis ash compositions for an accreting neutron star. Diffusion of oxygen, in a predominantly selenium crystal, is remarkably fast, comparable to diffusion in the liquid phase. We find a somewhat lower melting temperature for the oxygen-selenium system than that predicted by Medin and Cumming. This is probably because of electron screening effects.
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Schneider, A. S., Hughto, J., Horowitz, C. J., & Berry, D. K. (2012). Direct molecular dynamics simulation of liquid-solid phase equilibria for two-component plasmas. Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 85(6), 066405. http://dx.doi.org/10.1103/PhysRevE.85.066405
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© 2012 American Physical Society
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Article