I have a few questions/clarifications regarding the compatibility scheme in MP and pymatgen. If I understand correctly, when we use the MPCompatibility to process computed entries, for oxides, the scheme developed in this paper (https://journals.aps.org/prb/abstract/10.1103/PhysRevB.84.045115) is used. Here, two corrections are being done : The DFT overbinding problem of O2 molecule is treated the same way as the previous paper (https://journals.aps.org/prb/abstract/10.1103/PhysRevB.73.195107) and this correction is applied to oxide entries per oxygen atom on all of the oxides. Then, for transition metals with Hubbard U values, the mixing scheme correction of GGA / GGA+U is applied and this correction is per metal atom.
Is it correct that the GasCorrection scheme (of shifting the O2 molecule energy to fit the experimental value) is not done for oxides and AnionCorrection is used instead? On the other hand, nitrides, halides and hydrides use this GasCorrection to shift the DFT-calculated gaseous entry energies, and do not use the shifting of solid energies per O-atom as done in oxides?
If I understood correctly that in oxides instead of just shifting the O2 energy, we shift all of the oxide energies per O-atom, then for the O2 molecule energy, the raw DFT value would be used in generating the phase diagrams without any corrections?
Also, I guess this shifting energy has been determined separately for oxides, peroxides, superoxide and ozonides (as listed in MPCompatibility.yaml file), and this is named AnionCorrection? I just want to make sure, since both of the papers linked above didn’t do fitting for peroxides, superoxide. Is there a reference for this fitting?
Are the values The Advanced - U Corrections in MPCompatibility.yaml - exclusively for oxides?
Lastly, when generating MP entries to make phase diagrams, can we safely think of the most stable O2 entry (mp-12957) as the O2 molecule energy? The reason for this question is because this entry is tagged as “Oxygen - eta phase High pressure experimental phase”, a solid phase. Perhaps it’s because the entry that seems like O2 molecule (mp-1009490) is only 2 meV/atom above the hull (mp-12957), so either way is fine?