| Abstract Scope |
The Gibbs free energy encodes every material property, making phase diagrams the gold standard for assessing interatomic potentials. However, free-energy errors from DFT and fitting inhibit phase diagram accuracy and are invisible to energy/force benchmarks. We present a generalized method, exact in the infinite-sampling limit, for calculating atomistic phase diagrams without entropy truncation, analytical fitting, or on-lattice constraints. By connecting endpoint Frenkel-Ladd free energies to semigrand MD/MC integration via Henry’s Law, we directly sample classical entropy with full coupling, anharmonicity, and short-range-ordering. This exactness enables thermodynamic self-consistency conditions that identify missing features in interatomic potentials and circumvent DFT functional inaccuracies. We reproduce an AgCu EAM phase diagram exactly, and extend to AuPt and NiCr with first-principles MLIPs. In AuPt, endpoint anchoring overcomes established ~200 K PBE underbinding to reproduce the experimental diagram. In NiCr, we demonstrate that FCC SRO, arising from the Ni2Cr intermetallic, is required for agreement with experiment. |