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arXiv · 1905.08911

High temperature ion-thermal behavior from average-atom calculations

Damian C. Swift·Mandy Bethkenhagen·Alfredo A. Correa·Thomas Lockard·Sebastien Hamel·Lorin X. Benedict·Philip A. Sterne·Bard I. Bennett
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Abstract

Atom-in-jellium calculations of the Einstein frequency were used to calculate the mean displacement of an ion over a wide range of compression and temperature. Expressed as a fraction of the Wigner-Seitz radius, the displacement is a measure of the asymptotic freedom of the ion at high temperature, and thus of the change in heat capacity from 6 to 3 quadratic degrees of freedom per atom. A functional form for free energy was proposed based on the Maxwell-Boltzmann distribution as a correction to the Debye free energy, with a single free parameter representing the effective density of potential modes to be saturated. This parameter was investigated using molecular dynamics simulations, and found to be ~0.2 per atom. In this way, the ion-thermal contribution can be calculated for a wide-range equation of state (EOS) without requiring a large number of molecular dynamics simulations. Example calculations were performed for carbon, including the sensitivity of key EOS loci to ionic freedom.

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Damian C. Swift, Mandy Bethkenhagen, Alfredo A. Correa, Thomas Lockard, Sebastien Hamel, Lorin X. Benedict, Philip A. Sterne, Bard I. Bennett. 2019-05-22. High temperature ion-thermal behavior from average-atom calculations. https://doi.org/10.1103/physreve.101.053201

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