First-principles Equation of State and Shock Compression Predictions of Warm Dense Hydrocarbons

Abstract

We use path integral Monte Carlo and density functional molecular dynamics to construct a coherent set of equation of state for a series of hydrocarbon materials with various C:H ratios (2:1, 1:1, 2:3, 1:2, and 1:4) over the range of $0.07-22.4$ g/cm${}^3$ and $6.7\times 10^3-1.29\times 10^8$ K. The shock Hugoniot curve derived for each material displays a single compression maximum corresponding to $K$-shell ionization. For C:H=1:1, the compression maximum occurs at 4.7-fold of the initial density and we show radiation effects significantly increase the shock compression ratio above 2 Gbar, surpassing relativistic effects. The single-peaked structure of the Hugoniot curves contrasts with previous work on higher-$Z$ plasmas, which exhibit a two-peak structure corresponding to both $K$- and $L$-shell ionization. Analysis of the electronic density of states reveals that the change in Hugoniot structure is due to merging of the $L$-shell eigenstates in carbon, while they remain distinct for higher-$Z$ elements. Finally, we show that the isobaric-isothermal linear mixing rule for carbon and hydrogen EOSs is a reasonable approximation with errors better than 1% for stellar-core conditions.

7 pages, 4 figures. Accepted by Physical Review E

References in corpus (5)

• All-Electron Path Integral Monte Carlo Simulations of Warm Dense Matter: Application to Water and Carbon Plasmas
• First Principles Calculations of Shock Compressed Fluid Helium
• First-Principles Prediction of the Softening of the Silicon Shock Hugoniot Curve
• Equation of state for partially ionized carbon at high temperatures
• Ab initio calculation of thermodynamic, transport, and optical properties of CH${}_2$ plastics

Cited by in corpus (3)

• Path integral Monte Carlo simulations of dense carbon-hydrogen plasmas
• Equation of state of warm-dense boron nitride combining computation, modeling, and experiment
• Pauli Blocking in Degenerate Plasmas and the Separable Potential Approach