Method & caveats

Each MLIP generates low-index facets of every elemental ground state (pymatgen SlabGenerator, min slab 30 Å / min vacuum 10 Å, all terminations), relaxes the bulk (cell + ions) and each slab (fixed-cell, ions-only) under ASE FIRE, and the clean surface energy is γ = (E_slab − N·µ_bulk) / 2A. Accuracy is scored on the minimum-γ converged termination per facet, matched to the PBE Materials-Project / Crystalium reference on (element, Miller index). The headline surface γ MAE is the mean |Δγ| over DFT-matched facets; RMSE exposes the heavy error tail and MBE the near-universal under-prediction. All numbers measure agreement with PBE, not physical accuracy. Full protocol, metric definitions and caveats: Surface-energy methodology →.