Molecular-Brownian Correspondence in the Hard-sphere Dynamic Universality Class

We perform systematic simulation experiments on model systems with soft-sphere repulsive interactions to test the predicted dynamic equivalence between soft-sphere liquids with similar static structure. For this we compare the simulated dynamics (mean squared displacement, intermediate scattering function, {\alpha}-relaxation time, etc.) of different soft-sphere systems, between them and with the hard-sphere liquid. We then show that the referred dynamic equivalence does not depend on the (Newtonian or Brownian) nature of the microscopic laws of motion of the constituent particles, and hence, applies independently to colloidal and to atomic simple liquids. In addition, we verify another more recently-proposed dynamic equivalence, this time between the long-time dynamics of a Brownian fluid and its corresponding atomic liquid (i.e., the atomic system with the same interaction potential).