  Three structural populations with distinct average mobility are identified
within an equilibrium two-dimensional Lennard-Jones fluid simulated via
molecular dynamics at a constant temperature and varying density. Quantifying
the structure of the immediate neighborhood of particles by a tessellation
allows us to identify three distinct structural states by the shapes of the
tessellation cells. Irrespective of dynamic particle exchange among these
populations, each is observed to maintain their own thermodynamic and average
dynamic properties across the liquid-solid transition. We expect these findings
to be valuable for better understanding the structural basis of dynamical
heterogeneity in complex fluids defined in terms of local mobility
fluctuations.
