Thermophysical properties of warm dense hydrogen using quantum molecular dynamics simulations

We study the thermophysical properties of warm dense hydrogen by using quantum molecular dynamics simulations. Results are presented for the pair distribution functions, the equation of state, and the Hugoniot curve. From the dynamic conductivity, we derive the dc electrical conductivity and the reflectivity. We compare with available experimental data and predictions of the chemical picture. In particular, we discuss the nonmetal-to-metal transition, which occurs at about 40 GPa in the dense fluid.

Figure 1

(Color online) Proton-proton pair distribution function and corresponding coordination numbers according to Eq. (2) for 1000 K and three densities.

Figure 2

(Color online) Proton-proton pair distribution function and corresponding coordination numbers according to Eq. (2) for $0.5\text{g}/{\text{cm}}^3$ and three temperatures.

Figure 3

(Color online) Ratio of hydrogen molecules with respect to the total number of protons for three densities: our coordination number method (solid line) is compared with the pair-counting method of Vorberger et al. (Ref. 23) (dotted line). Their result, which counts only pairs with a lifetime longer than ten ${\text{H}}_2$ vibrational periods, is also given (dashed line).

Figure 4

Thermal EOS for warm dense hydrogen (pressure isotherms): QMD data are compared with the chemical models ${\text{FVT}}^{+}$ (Ref. 50) and SCvH-i (Ref. 51).

Figure 5

(Color online) Principal Hugoniot curve for hydrogen: results of this work (solid line) are compared with previous QMD results of Lenosky et al. (Ref. 58) (dashed line) and Desjarlais (Ref. 22) (stars), PIMC simulations (Ref. 62) (dotted line), the linear mixing model of Ross (Ref. 60) (dot-dash-dashed line), the model EOS of Kerley (Ref. 61) (dot-dot-dashed line), and the chemical model FVT (Ref. 48) (dot-dashed line). Experiments: gas gun (Ref. 56) (diamonds), Sandia Z machine (Ref. 8) (gray squares; gray line: running average through the $u_s-u_p$ data), and high explosives (Ref. 57) (black circles).

Figure 6

(Color online) dc conductivity for hydrogen: QMD results along the Hugoniot curve and along three isotherms are compared with the single shock data of Nellis et al. (Ref. 14) and multiple shock data of Weir et al. (Ref. 15). Earlier QMD results of Collins et al. (Ref. 12) are also shown.

Figure 7

(Color online) Reflectivity for a wavelength of 808 nm along the Hugoniot curve of hydrogen: QMD results are compared with the experimental data of Celliers et al. (Ref. 66) and predictions of the chemical model FVT (Ref. 67) by using the COMPTRA code (Ref. 68) and QMD simulations of Collins et al. (Ref. 20).