Comparison of Various Potential Models for the Simulation of the Pressure of Liquid and Fluid N₂

Abstract

We have performed molecular dynamics (MD) calcuations with 256 particles to simulate the pressure of liquid and fluid nitrogen in the low and the high pressure regions. The pressure in MD calculations is extremely sensitive for the form of the potential employed and therefore this quantity is best suited to test intermolecular potentials. We have studied eight different potential models including a three-body potential. Of the potential functions considered, the existing purely effective Lennard-Jones (LJ) potentials- 1-centre and 2-centres-do not suffice to give the experimental pressure for the whole pressure range. The 2-LJ-centres models derived from potential hypersurfaces calculated by “ab initio” methods produce slightly better results and led to an optimal model potential which reflects the experimental data within the statistical error of the MD. The 2-LJ centres model potential function we used for the fit cannot model the fine structure of the “ab initio” calculated hypersurface, but describes it in a balanced way when the higher energies are excluded systematically. We have achieved this by a certain weighting procedure.