  First-principles molecular dynamics (FPMD) simulations are performed on 6 and
12% Na in dense liquid N. A detailed description of structural and electronic
properties leading to an understanding of the effect of Na-doping on the
polymerization phase transition of N is presented. Compression of the mixtures
from 5 to 90 GPa shows three distinct regions of characteristic local order
separated by pressures near 30 and 65 GPa. Computation of Gibbs free energies
of mixing shows that these mixtures are thermodynamically stable beyond 20 and
15 GPa for 6 and 12 % Na respectively.
