Energetics and stability of diamondlike amorphous carbon

Simulations of diamondlike amorphous carbon formed by quenching the liquid under high pressure indicate that two distinctly different dense phases exist. The ``as-quenched'' phase is metastable and mostly fourfold coordinated. Upon annealing, it converts into a more stable structure with the majority of atoms having threefold coordination. Both structures are consistent with experimental findings. The annealed phase is clearly distinguished from the low-coordinated network of evaporated -C.