Novel sp3 forms of carbon predicted by evolutionary metadynamics and analysis of their synthesizability using transition path sampling

摘要

Experiments on cold compression of graphite have indicated the existence of a new superhard and transparent allotrope of carbon. Numerous metastable candidate structures featuring different topologies have been proposed for “superhard graphite”, showing a good agreement with experimental X-ray data. In order to determine the nature of this new allotrope, we use evolutionary metadynamics to systematically search for low-enthalpy sp³ carbon structures easily accessible from graphite and we employ molecular-dynamics transition path sampling to investigate the corresponding kinetic pathways starting from graphite at 15–20 GPa. Real transformation kinetics are computed and physically meaningful transition mechanisms are produced at the atomistic level of detail in order to demonstrate how nucleation mechanism and transformation kinetics lead to M-carbon as final product of cold compression of graphite. This establishes M-carbon as an experimentally synthesized carbon allotrope.