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

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.