Complex Behavior of Fluid Lithium under Extreme Conditions

Lithium is a prototypical simple metal at standard conditions which is well described within the nearly free electron model. However, by changing the density towards expanded or compressed states, the electrical conductivity shows strong and partly unexpected variations. We have performed quantum molecular dynamics simulations for fluid lithium for a wide range of densities and temperatures in order to derive the equation of state, the electrical conductivity, and information about structural and electronic changes along the expansion or compression. Based on these results, we can give a consistent description of the electrical conductivity from the nonmetallic expanded fluid up to the degenerate electron liquid at high densities.

Figure 1

Electrical conductivity of shock-compressed Li [6] compared with QMD simulations. The temperatures and densities (in $\mathrm{g}/{\mathrm{cm}}^3$) of the QMD calculations are indicated.

Figure 2

Electrical conductivity of shock-compressed Li [4, 5] compared with isotherms derived from QMD simulations. We have added the 7000 K data points from Fig. 1.

Figure 3

General behavior of the electrical conductivity of fluid Li from low up to ultrahigh densities for various temperatures. EF: expanded fluid; FM: fluid metal; DEL: degenerate electron liquid.

Figure 4

Density of states in fluid Li at 2000 K for a sequence of densities with the Fermi energy located at zero energy. Increasing density leads to a strong reduction of the DOS at the Fermi level which is typical for a dirty metal. In the high-density limit, the DOS is almost constant which underlines the nonsimple metal behavior in this highly correlated region.

Figure 5

Ion-ion pair correlation function in fluid Li at 2000 K for a sequence of densities.

Figure 6

Variation of the charge density in fluid Li at 2000 K in units of $e/{\AA }^3$ for a sequence of densities ($0.12\mathrm{g}/{\mathrm{cm}}^3$ upper left to $10.0\mathrm{g}/{\mathrm{cm}}^3$ lower right). The $x$ and $y$ axis are also given in units of Å. The charge density plots are taken from typical snapshots of the QMD run. We have selected representative planes through the simulation box parallel to the $xy$ plane.