Simulation of solidα-nitrogen

The molecular dynamics method is used to simulate a fcc solid of 500 nitrogen molecules interacting by an atom-atom potential. Translational and rotational order parameters are computed, showing the existence of a crystal plastic phase not far from the coexistence line of the $\alpha$ and $\beta$ phases. Molecular pair distribution functions are calculated, and it is shown that thermodynamics quantities cannot be given with precision by the molecular dynamics method. Correlation functions are described. A link is established between the correlation functions and the language of phonons. The spectrum of the phonon frequencies is computed for six thermodynamic states, and the domain of validity of the harmonic approximation is discussed.