A crossover from metal to plasma in dense fluid hydrogen

Thermodynamic properties in dense fluid hydrogen are studied by using a density-functional theory for electron-proton binary mixtures that is called quantal hypernetted-chain (QHNC) integral equation. A nonlocal approximation for the exchange-correlation potential in a finite-temperature Kohn-Sham equation is presented. Results obtained from the QHNC with the nonlocal approximation are compared with those obtained from the QHNC with a local density approximation. Temperature variation of thermodynamic quantities between 10(4) and 10(6) K are investigated along an isochor specified by a dimensionless density parameter of rs=0.5. These quantities obtained from the QHNCs show that a crossover from metal to plasma occurs around a temperature of T=1.78 x 10(5) K. Electrical resistivity Re of the dense fluid hydrogen evaluated from a Ziman formula [The Properties of Liquid Metals, edited by S. Takenohi (Wiley, New York, 1973)] extended to finite temperature is about 0.7 muOmega cm at T=10(4) K. The dense fluid hydrogen at the temperature can be considered as a metallic fluid, because the value is smaller than typical values of Re in alkali metals at room temperature. The Re slightly increases with the temperature increase, and the temperature valuation of Re is monotonic. We clearly show that the contribution from the electronic excited states plays an important role for the sharp crossover from the metal to the plasma, and that the crossover is interpreted as a crossover from degenerate electron gas to nondegenerate electron gas.