Constraints, metastability, and inherent structures in liquids

Void-size distributions have been calculated for the shifted-force Lennard-Jones fluid over substantial temperature and density ranges, both for the liquid-state configurations themselves, as well as for their inherent structures (local potential energy minima). The latter distribution is far more structured than the former, displaying fee-like short-range order, and a large-void tail due to system-spanning cavities. Either void distribution can serve as the basis for constraints that retain the liquid in metastable states of superheating or stretching by eliminating configurations that contain voids beyond an adjustable cutoff size. While acceptable cutoff sizes differ substantially in the two versions, ranges of choices have been identified yielding metastable equations of state that agree between the two approaches. Our results suggest that the structure-magnifying character of configuration mapping to inherent structures may be a useful theoretical and computational tool to identify the low-temperature mechanisms through which liquids and glasses lose their mechanical strength.