Ab initio study of the structures and transport properties of warm dense nitrogen

Using ab initio molecular dynamics simulations, detailed ionic structures and transport properties of warm dense nitrogen have been investigated in the density and temperature ranges of 1.5-3.0 g cm(-3) and 1000-50,000 K, respectively. The simulations find that the nitrogen molecules primarily dissociate at temperatures above 10,000 K along the isotherms and Hugoniot in the warm dense matter regime, and a few different size-scale clusters form. The dissociations have a dominant effect on the electrical and thermal conductivities, and the contributions of the clusters to the transport properties are not negligible. Additionally, detailed simulations of the behavior of the electrical and thermal conductivities of warm dense nitrogen indicate that nitrogen is metallic at pressures above 60 GPa. This phenomenon has also been explored from the standpoint of the Wiedemann-Franz law, which is consistent with the calculation of the electrical conductivity for metallic pressures. The present simulation results provide a valuable reference for future experimental and theoretical modeling studies.