Dependence on the thermodynamic state of self-diffusion of pseudo hard-spheres

TL;DR

This paper investigates how the self-diffusion coefficient in pseudo hard-sphere systems depends on thermodynamic state variables, using molecular dynamics simulations to analyze the effects of damping and noise.

Contribution

It introduces a hypothesis linking self-diffusion to a thermodynamic function and confirms it through simulations showing the independence of this function from noise intensity.

Findings

The diffusion coefficient scales with concentration as hypothesized.

Noise intensity affects the baseline diffusivity but not the thermodynamic function.

The thermodynamic function remains invariant under different damping and noise conditions.

Abstract

Self-diffusion, $D$, in a system of particles that interact with a pseudo hard sphere potential is analyzed. Coupling with a solvent is represented by a Langevin thermostat, characterized by the damping time $t_d$. The hypotheses that $D=D_0 \varphi$ is proposed, where $D_0$ is the small concentration diffusivity and $\varphi$ is a thermodynamic function that represents the effects of interactions as concentration is increased. Molecular dynamics simulations show that different values of the noise intensity modify $D_0$ but do not modify $\varphi$. This result is consistent with the assumption that $\varphi$ is a thermodynamic function, since the thermodynamic state is not modified by the presence of damping and noise.