Improved electron-gas model calculations of solid N2 to 10 GPa

Recently, LeSar and Gordon [J. Chem. Phys. 78, 4991 (1983)] reported calculations of the crystal structures of solid N2 and CO2 to 10 GPa using electron-gas short-range energies and pairwise dispersion energies that included only the anisotropic C6/r6 term. While the calculated zero temperature pressure-volume curve was in excellent agreement with the experimental results, the structure that was calculated to be most stable at high pressure (the β-O2 structure with space group R3̄m) is not consistent with experimental spectroscopic results. Here we report calculations on solid N2 using a pairwise damped-dispersion energy that includes terms up to C10/r10. While we fail to predict the low pressure, low temperature Pa3(α)–P42/mnm(γ) transition, we find a transition from the P42/mnm structure to one with a space group R3̄c at 1.9 GPa, in agreement with the experimental transition pressure. The calculated structure is consistent with the high pressure experimental results. Possible distortions of the R3̄c to a R3c structure were examined, but no distortions were found to 75 GPa.