On-the-fly machine learning augmented constrained molecular dynamics to design routes from glassy carbon to quenchable amorphous diamond
Phys. Rev. B 112, 094207 – Published 29 September, 2025
DOI: https://doi.org/10.1103/lzhy-7xd4
Abstract
Recent experiments reveal critical roles of anisotropic stresses in transforming glassy carbon (GC) into amorphous diamond, yet ab initio molecular dynamics (AIMD) softwares handling such situations remain scarce. Here, we develop an on-the-fly machine learning augmented constrained AIMD (ML-augmented CAIMD) method by modifying standard AIMD, enabling fast GC simulations under anisotropic stresses and capturing its structural complexity via iterative ML potential updates. Using this approach, new routes from GC to quenchable amorphous diamond with easy synthesis conditions are searched, where the effect of severe rotational shear strains on stabilizing bonds, previously overlooked in synthesis processes, is now considered. We first demonstrate that GC has unexpectedly high plasticity in ambient conditions, with its tensile strength kept constant up to a strain of 0.6 and its compression and shear strengths stiffened by large strains. Under pressure, increasing annealing temperature promotes the formation of quenchable amorphous diamond by enhancing preservation upon decompression, but this trend reverses above 2900 K due to thermal graphitization. Remarkably, we find that severe rotational shear strains applied under a pressure of 30 GPa can promote high hybridization (up to 80%) at low temperatures , which are quenchable to ambient conditions. A hardened amorphous carbon structure retaining a substantial fraction of 64% is obtained by decompression from 30 GPa pressuring at 300 K after applying a rotational shear strain of 1.0, the lowest pressure and temperature ever predicted. Our on-the-fly ML-augmented CAIMD algorithm enables designing synthesis routes for quenchable amorphous carbon under unexplored conditions and offers a general framework for structural transformations in disordered materials under extreme conditions and anisotropic stresses.
