Thermodynamic and Dynamic Anomalies for Dumbbell Molecules Interacting with a Repulsive Ramp-Like Potential

TL;DR

This study uses discrete molecular dynamics to explore thermodynamic and dynamic anomalies in dumbbell molecules with a repulsive ramp potential, revealing behaviors similar to water and dependence on potential discretization.

Contribution

It demonstrates how the number of steps in the discretized potential affects thermodynamic and dynamic anomalies in dumbbell molecules.

Findings

Both systems show density maxima and mobility anomalies.

Mobility behaviors resemble those of water, with non-monotonic trends.

Anomalies depend strongly on the discretization parameter n.

Abstract

Using collision driven discrete molecular dynamics (DMD), we investigate the thermodynamics and dynamics of systems of 500 dumbbell molecules interacting by a purely repulsive ramp-like discretized potential, consisting of $n$ steps of equal size. We compare the behavior of the two systems, with $n = 18$ and $n = 144$ steps. Each system exhibits both thermodynamic and dynamic anomalies, a density maximum and the translational and rotational mobilities show anomalous behavior. Starting with very dense systems and decreasing the density, both mobilities first increase, reache a maximum, then decrease, reache a minimum, and finally increase; this behavior is similar to the behavior of SPC/E water. The regions in the pressure-temperature plane of translational and rotational mobility anomalies depend strongly on $n$. The product of the translational diffusion coefficient and the orientational correlation time increases with temperature, in contrast with the behavior of most liquids.