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DOE OSTI · 1841327

High-temperature ion-thermal behavior from average-atom calculations

Swift, Damian C.·Bethkenhagen, Mandy·Correa, Alfredo A.·Lockard, Thomas·Hamel, Sebastien·Benedict, Lorin X.·Sterne, Philip A.·Bennett, Bard I.
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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 six to three 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. Finally, 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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Swift, Damian C., Bethkenhagen, Mandy, Correa, Alfredo A., Lockard, Thomas, Hamel, Sebastien, Benedict, Lorin X., Sterne, Philip A., Bennett, Bard I.. 2020-05-04. High-temperature ion-thermal behavior from average-atom calculations. https://doi.org/10.1103/physreve.101.053201

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