Molecular Dynamic Study of Liquid Nitromethane under High-Pressure

The thermodynamic properties of liquid nitromethane under high-pressure have been determined using molecular dynamic (MD) simulations based on classical empirical potentials and first-principles Car-Parrinello method (CPMD). Classical MD simulations were carried out to study the structural and thermodynamics properties of nitromethane under high pressure, and the theoretical Hugoniot was obtained up to 14.2 GPa. For some thermodynamic functions, such as total energy, particle velocity, the classical MD simulations agree well with experimental results. However, it predicts a higher Hugoniot pressure at given density. The CPMD simulations were performed at several selected densities. The radial pair correlation functions, velocity auto-correlation functions, vibration spectra, and other thermodynamic properties have been obtained and compared with the results of classical MD. The careful analysis of the pair correlation functions reveals that the short-range part of the classical potential may be too stiff. There are substantial differences for pair correlation functions between CPMD and classical simulations, while such difference can be attributed as quantum effects. The vibration spectra of liquid nitromethane were obtained from CPMD simulations at ambient conditions and at high pressure. The pressure-induced shifts of vibrations to high frequency predicted by CPMD are consistent with the experimental observation.