Synthesis of the post-diamond BC8 phase of carbon

Uncovering the behavior of carbon under extreme pressures and temperatures is crucial for understanding the interiors of carbon-rich exoplanets and harnessing ablator materials for inertial confinement fusion. Recent advancements in powerful laser compressions, in-situ X-ray diffraction, and exascale supercomputers have opened a new era of materials exploration with unprecedented detail. In this talk, I will highlight transformative advances in predicting the synthesis pathways toward the elusive high-pressure BC8 post-diamond phase of carbon, revealed through quantum-accurate, billion-atom molecular dynamics shock simulations conducted on the DOE's exascale supercomputer, Frontier. By leveraging machine-learning interatomic potentials and the world's most powerful computer, we simulate atomic-scale dynamics at experimental time (nanosecond) and length (micrometer) scales. These groundbreaking simulations are being validated through an experimental campaign at the National Ignition Facility.