Hexagonal diamond formation mechanism: A review

As a metastable carbon allotrope, hexagonal diamond (HD) exhibits potentially superior mechanical properties to cubic diamond (CD). However, its synthesis faces significant thermodynamic and kinetic challenges. This review summarizes the critical role of computational simulations in the synthesis of HD, covering both static calculations and molecular dynamics (MD) simulations. Static calculations reveal that graphite tends to transform into CD under interface-free conditions, whereas the presence of an interface results in a lower energy barrier for the HD phase transition. With regard to MD simulations, while early shock compression simulations failed to observe HD formation, recent studies based on neural network potentials have confirmed a shock-velocity-dependent transformation pathway and have successfully obtained HD, consistent with in situ experimental results. Hydrostatic pressure simulations emphasize the importance of controlling interlayer sliding, demonstrating that strategies such as quasi-uniaxial compression can promote the preferential formation of HD. In the future, the integration of high-precision simulations with experimental approaches is expected to enable the controllable synthesis of HD, thereby advancing its applications in ultrahard materials, power electronics, aerospace, and other fields.