MP2020 Compatibility

Goal

To apply Materials Project 2020 Compatibility schemes to MLIP-predicted energies. This is required for models trained on GGA/GGA+U mixed data (e.g., MPtrj data) when constructing convex hulls or phase diagrams to ensure compatibility with the Materials Project database.

[!IMPORTANT] Do NOT apply this to r2SCAN models. Only use this for models trained on GGA/GGA+U mixed data.

Scientific Context

Why is this needed?

The Materials Project (MP) database mixes calculations from two levels of theory: GGA (PBE) and GGA+U. Transition metals (e.g., Mn, Fe, Co, Ni) are calculated with a Hubbard U correction only when present in oxides or fluorides; otherwise, they use standard PBE. To construct a unified convex hull, MP applies the MP2020 Compatibility scheme (energy shifts) to align these distinct potential energy surfaces.

MLIPs trained on MP data (e.g., MACE-MP-0) typically learn these mixed energies. To accurately predict stability against the MP hull, one must apply the same MP2020 corrections to the MLIP outputs.

Potential Issues

Selective application of U introduces discontinuities in the Potential Energy Surface (PES) that are difficult for MLIPs to model physically.

• Artifacts: Models may exhibit spurious repulsion or underbinding between U-corrected metals and ligands, as they interpolate between incompatible GGA and GGA+U regimes.