Molecular dynamic program for simulation of molecular nitrogen N2 properties under high pressure

Molecular dynamic simulation program has been developed which can be used to model the static and dynamic properties of molecular nitrogen (N2) under high pressure. The dynamics of the N2 molecules accounts precisely both translational and rotational degrees of freedom. The rotational motion of the N2 molecule is approximated assuming constant moment of inertia of the nitrogen molecule. The program fully accounts anisotropic N2-N2 interaction potential. N2-N2 interaction potential has been based on the results of high precision Hartree-Fock ab initio quantum mechanical calculations of van der Avoird et al [1]. The seven parameter potential form, fully accounting rotational symmetry of the N2-N2, using 6-j Wigner symbol, thus preserving full rotational symmetry of the system, was used [1]. Various numerical algorithms were tested, with respect to energy preservation during the simulation. It has been shown that Verlet algorithm was not preserving the energy for the standard timestep, equal 5 *10 s. Runge-Kutta fourth order method was able to preserve the energy within 10 relative error, but it requires calculation of the force four time for the timestep and therefore it is inefficient. A predictor-corrector method of the 5 order was found to be efficient and precise and was therefore adopted for the simulation of the molecular nitrogen properties at high pressure. Joint 20 AIRAPT – 43 EHPRG, June 27 – July 1, Karlsruhe/Germany 2005