Fig. 3: Simulation evidence for the ground-state degeneracy.

a A small part of the representative snapshot for the most stable structure determined by the replica exchange molecular dynamics simulation. The green and red frames mark different local configurations in Fig. 2d, and the blue frames illustrate the existence of meta-space-filling structures at finite temperatures. Red and green have the same meaning as in Fig. 2d, while we do not distinguish red and purple here. b Amorphization process characterized by the decay of bond-orientational order parameter \(|{\varPsi }_{4}|\) at three temperatures below the melting point. The inset is a small part of the snapshot at T = 2.86 after amorphization. c Caloric curve (potential energy \({E}_{{{{\rm{p}}}}}\) versus temperature T) and density curve (density \(\rho\) versus T), both with the discontinuous changes located at T = 2.88‒2.89. The error-bars represent standard deviations, resulting from the thermal fluctuations in one simulation trajectory. d Time evolution of the unit-cell order parameter d in the simulation starting from a locally disordered crystalline structure at T = 2.83, 2.86, and 2.88. Each curve plotted in b and d is based on the data from a single simulation. Due to the randomness of the dynamical process, the starting point and the rate of amorphization may take different values in different trajectories. Physical quantities are expressed in L-J units.