Equations of state, transport properties, and compositions of argon plasma: Combination of self-consistent fluid variation theory and linear response theory

A consistent theoretical model that can be applied in a wide range of densities and temperatures is necessary for understanding the variation of a material's properties during compression and heating. Taking argon as an example, we show that the combination of self-consistent fluid variational theory and linear response theory is a promising route for studying warm dense matter. Following this route, the compositions, equations of state, and transport properties of argon plasma are calculated in a wide range of densities $(0.001-20\mathrm{g}/\mathrm{c}{\mathrm{m}}^3)$ and temperatures $(5-100\mathrm{kK})$. The obtained equations of state and electrical conductivities are found in good agreement with available experimental data. The plasma phase transition of argon is observed at temperatures below $30\mathrm{kK}$ and density about $2-6\mathrm{g}/\mathrm{c}{\mathrm{m}}^3$. The minimum density for the metallization of argon is found to be about $5.8\mathrm{g}/\mathrm{c}{\mathrm{m}}^3$, occurring at $30-40\mathrm{kK}$. The effects of many-particle correlations and dynamic screening on the electrical conductivity are also discussed through the effective potentials.

Figure 1

Hugoniots of liquid argon as predicted by SFVT using ab initio and EXP-6 potential. The experimental data are taken from Refs. [51, 52, 53].

Figure 2

Shock temperature and degree of ionization of liquid argon along the Hugoniots from the same initial state as in Fig. 1.

Figure 3

Isotherms of pressure for argon plasma at different temperatures. Solid lines: considering the lowering of ionization potential. Dashed lines: without the lowering of ionization potential for $5,20,30,\mathrm{and}100\mathrm{kK}$, as representatives. Please note that the pressure scale for the lowest four temperatures (right scale) is different from that for higher temperatures (left scale) for clarity.

Figure 4

Derivatives of pressure with respect to density are shown as a function of density at different temperatures. It drops at about $5\mathrm{g}/\mathrm{c}{\mathrm{m}}^3$ as an indication of the plasma phase transition.

Figure 5

Compositions of argon plasma versus density at different temperatures. (a) Fraction of electron, (b) fraction of Ar, (c) fraction of $\mathrm{A}{\mathrm{r}}^{+1}$, and (d) fraction of $\mathrm{A}{\mathrm{r}}^{+2}$. The thick black line in panel (a) is a link of all the minima of degree of ionization, indicating the onset of pressure ionization.

Figure 6

Compositions of argon plasma given by SFVT are compared with those given by comptra04 at four different temperatures. The data of comptra04 are taken from the website [56].

Figure 7

Isotherms of electrical conductivity at different temperatures. Solid lines: SFVT+LRT. Dashed lines: Results of comptra04 [56] at three temperatures. Symbols: data of gas gun and explosive experiments [57, 58, 59].

Figure 8

Electrical conductivity versus temperature at different densities for argon plasma.

Figure 9

Thermal conductivity versus density at different temperatures for argon plasma together with those given by comptra04 [56].

Figure 10

Thermopower versus density at different temperatures for argon plasma. (a) Results of this work (SFVT+LRT); (b) comparison with comptra04 [56].

Figure 11

Effects of many-particle correlations on the electrical conductivity of argon.

Figure 12

Effects of dynamic screening on the electrical conductivity of argon.