Dynamic transitions in molecular dynamics simulations of supercooled silicon

Two dynamic transitions or crossovers, one at a low temperature (T* approximate to 1006 K) and the other at a high temperature (T-0 approximate to 1384 K), are shown to emerge in supercooled liquid silicon using molecular dynamics simulations. The high-temperature transition (T-0) marks the decoupling of stress, density, and energy relaxation mechanisms. At the low-temperature transition (T*), depending on the cooling rate, supercooled silicon can either undergo a high-density-liquid to low-density-liquid (HDL-LDL) phase transition or experience an HDL-HDL crossover. Dynamically heterogeneous domains that emerge with supercooling become prominent across the HDL-HDL transition at 1006 K, with well-separated mobile and immobile regions. Interestingly, across the HDL-LDL transition, the most mobile atoms form large prominent aggregates while the least mobile atoms get spatially dispersed akin to that in a crystalline state. The attendant partial return to spatial uniformity with the HDL-LDL phase transition indicates a dynamic mechanism for relieving the frustration in supercooled states.