Self-consistent phonon calculation of the elastic constants of the β phase of solid N2

The self-consistent phonon approximation of anharmonic lattice dynamics is used to calculate the elastic constants of solid hcp β-N2. We have assumed completely disordered molecular orientations and a (12–6) Lennard–Jones intermolecular potential. Unlike previous work our calculations take explicit account of certain cubic anharmonic terms. Commonly accepted values of the intermolecular potential parameters give rise to triple point elastic constants that are in poor agreement with recent experimental values derived from Brillouin scattering in oriented single crystals. Calculations using intermolecular potentials derived from sphericalization of atom–atom potentials to be found in the recent literature yield equally poor results. Possible explanations for this are discussed.