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Updated: Dec 17, 2025

Non-equilibrium Microwave Plasma for Efficient High Temperature Chemistry
Published on: August 1, 2017
High-temperature ion-thermal behavior from average-atom calculations
Damian C Swift1, Mandy Bethkenhagen1, Alfredo A Correa1
1Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94551, USA.
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. 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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