PNNL

Abstract

Molecular Dynamics simulations utilizing a many-body potential was used to study the pressure dependence of structural and dynamical properties for liquid methanol. The liquid density as a function of pressure agreed quite well with experiment, and a combination of radial and angular distribution functions were used to analyze molecular structure. From these distribution functions, it was observed that hydrogen bond strength increased with increasing pressure. This observation coincided with an increase in the molecular dipole as a function of pressure, which would definitely have a significant effect on the observed increased hydrogen bond strength. Also, methanol molecules were shown to more strongly favor exactly two hydrogen bonds at higher pressures, while fewer methanols with either zero, one, or three hydrogen bonds were observed at higher pressures. Furthermore, a majority of the compression with increased pressure was found to occur in regions perpendicular to the methanol oxygen-hydrogen bond vector. The methanol translational diffusion decreased significantly with increased pressure, while the rotational diffusion decreased at a similar magnitude around the oxygen-hydrogen and oxygen-carbon bond vectors, despite having very different overall diffusion. Finally, the hydrogen bond lifetime increased significantly with pressure, owing to the increased hydrogen bond strength.