Three-Body Interactions and Shock Compression Properties of Condensed Nitrogen

Based on ab initio calculation of quantum-chemical theory, the repulsive potential among three nitrogen molecules (N2)3, as well as that between two nitrogens (N2)2, were calculated for a large amount of molecular directions from randomly sampling. The molecular distance and the geometry of the considered (N2)3 count the multi-body correlations in condensed nitrogen, and spherically averaged approximation of the orientation described the effect of high temperature. An analytic formula of the effective pair potential, which includes effects from various 3-body interactions, was proposed. It is found that three-body contribution obviously soften the average pair potential. The newly determined repulsive potential, combined with van der Waals long-range correlation, was used to predict Hugoniot curve of liquid nitrogen by the fluid-perturbation variational statistical theory. The good agreement between theoretical Hugoniot and the available experimental data indicates that the present scheme for the effective pair potential is reliable.