The role of the intermolecular potential in determination of equilibrium and dynamic properties of molecular nitrogen (N2) properties: MD simulations

Abstract

High precision approximation of the intermolecular potential is necessary for molecular dynamics (MD) simulations of the physical properties of molecular nitrogen (N2). Recently, Quantum Mechanical (QM) high precision calculations (coupled-cluster singles-and-doubles with a perturbative triples corrections [CCSD(T)]) were used to determine N2 - N2 intermolecular interaction. Using these data, the potential, covering all orientations of the pair of the nitrogen molecules, was obtained in the form invariant with respect of rotation of the reference system. The new N2-N2 potential remains in reasonably good agreement with the isotropically scaled potential function of van der Avoird et al, based on the results of Hartree–Fock calculations. Nitrogen equation of state, at pressures up to 30 GPa (300 kbar) and at temperatures from room temperature to 2000K, was obtained by MD simulations, employing the following potentials: the new CCSD(T) function, the nonscaled and scaled expression by van der Avoird et al., and four-atom interaction by Johnson et al. It was shown that the new potential gives considerably better agreement with the experimental data than in all other cases. MD simulations were also used to determine shear viscosity of nitrogen. It was shown that the influence on the potential variation on the MD obtained values of the viscosity is much stronger than on the equation of state, especially at higher densities. The results were compared with the experimentally measured values of the viscosity showing considerable difference between the date obtained from experiment and derived form MD simulations.