Molecular Dynamics Simulations of Warm Dense Carbon

HD Whitley and DM Sanchez and S Hamel and AA Correa and LX Benedict, CONTRIBUTIONS TO PLASMA PHYSICS, 55, 390-398 (2015).

DOI: 10.1002/ctpp.201400101

We present classical and DFT-based molecular dynamics (MD) simulations of carbon in the warm dense matter regime (rho= 3.7 g/cc, 0.86 eV < T < 8.62 eV T < 100 eV for classical MD). Two different classical interatomic potentials are used: 1. LCBOP, designed to simulate condensed (e.g. solid) phases of C, and 2. linearly screened Coulomb (Yukawa) potentials. It is shown that LCBOP over-predicts minima and maxima in the pair correlation functions of liquid-C in this regime when compared to the DFT-MD results. The screened Coulomb model, while under- correlating at low-T, seems to produce the correct qualitative features in the static ionic pair distributions at the highest-T. However, both approaches predict the decay in the ionic contribution of the specific heat as T -> infinity to be much slower than that predicted by a model based on DFT-MD. These differences in the MD-derived equations of state in warm dense regimes could have important consequences when using classical inter-ionic forces such as these in large-scale MD simulations aimed at studying, for instance, processes of relevance to inertial confinement fusion when C is used as an ablator material. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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