NVU view on energy polydisperse Lennard-Jones systems.

When energy polydispersity is introduced into the Lennard-Jones (LJ) system, there is little effect on structure and dynamics [T. S. Ingebrigtsen and J. C. Dyre, J. Phys. Chem. B 127, 2837 (2023)10.1021/acs.jpcb.3c00346]. For instance, at a given state point both the radial distribution function and the mean-square displacement as a function of time are virtually unaffected by even large energy polydispersity, which is in stark contrast to what happens when size polydispersity is introduced. We here argue-and validate by simulations of up to 30% polydispersity-that this almost invariance of structure and dynamics reflects an approximate invariance of the constant-potential-energy surface. Because NVU dynamics defined as geodesic motion at constant potential energy is equivalent to Newtonian dynamics in the thermodynamic limit, the approximate invariance of the constant-potential-energy surface implies virtually the same physics of energy polydisperse LJ systems as of the standard single-component version. In contrast, the constant-potential-energy surface is significantly affected by introducing size polydispersity.