Bonding interactions and carbon clustering in warm dense titanium carbide

While the phenomenon of diamond precipitation from carbon-based materials under high pressure/temperature conditions has been observed experimentally and modeled theoretically, the typical focus on hydrocarbon materials prompts a look at alternative carbon sources. We use density functional theory simulations to study the transition metal monocarbide TiC under extreme conditions. Elucidating the underlying bonding interactions in the ambient- and high-pressure polymorphs with chemistry-inspired tools reveals drastic differences in the crystals, with an absence of C-C interactions in the ambient-pressure phase contrasted by a robust covalently bound network of carbon at high pressure. In DFT-based molecular dynamics simulations of the high-pressure phase, these carbon chains persist upon melting. However, new C-C interactions develop at the onset of melting even in the ambient-pressure phase. This tendency towards carbon clustering in the melt signals the potential for diamond nucleation, motivating further study of a broader range of materials and more detailed knowledge of the nucleation mechanism.