Question about the MP-Advanced Correction value for Fe oxides

#1

Hello,

in order to understand the MP correction schemes for the formation energies of transition metal oxides I studied the PRB papers of Wang (2006) and Jain (2011), and used the total energies given on the MP pages first for Manganese oxides to reproduce the Advanced Correction value for Mn (-1.68 eV per Mn), which worked out perfectly. So I think I am applying the procedure correctly.

But applying the same method to the iron oxides (FeO, Fe2O3, Fe3O4) did not lead to the correction value of -2.733 eV per Fe which is given on the MP pages, but to -2.27 eV instead. I also found the information online, that Fe3O4 was excluded from the fitting, but this changed the value only to -2.24 eV. I used the experimental standard formation enthalpies as follows: FeO: -272 kJ/mol, Fe2O3: -824.2 kJ/mol, Fe3O4: -1118,4 kJ/mol. These values are taken from wikipedia, and they deviate only within 2 kJ/mol (or 0.02 eV/f.u.) from those given by the NIST Chemistry WebBook (webbook.nist.gov/chemistry) so I think they are reliable.

Using the correction value of -2.27 eV [A] reproduces the experimental values [E] much better as if I take the MP value of -2.733 eV:

FeO: -1.4097 [E], -1.4350 [A], -1.669 [MP]
Fe2O3: -1.7111 [E], -1.6986 [A], -1.886 [MP]
Fe3O4: -1.6596 [E], -1.6353 [A], -1.836 [MP]

All values are given in eV/atom. As said before, I only took MP total energies and applied the procedure of Jain (2011). So my question is whether I did a mistake here or the MP correction value for Fe is wrong, or if anything else was taken into account by MP which is not explained in the stated paper.

A reply would be highly appreciated.

#2

Hi Daniel, thanks for the detailed post. I’ve suspected there might be an issue with this for a little while, but didn’t have a hard example (or a potential cause) other than what I’d seen with some of the non-corrected compounds (e. g. RuO2 is also pretty far off). Unfortunately, most of the experts in the correction scheme aren’t frequent forum users. I think we might get better mileage consulting the pymatgen google group. Is it okay if I post your message there? Alternatively, you’re welcome to do it:

https://groups.google.com/forum/#!forum/pymatgen

Also, for anyone reading this thread, we’ll follow up here with any results we find.

#3

hi @danielr I am also trying to reproduce the correction value for Fe.
I want to make sure that I am doing correctly as in the paper Jain (2011).
Fe2O3: -1.7112 (exp), -1.8862 (theo_MP), 0.175 (exp-theo_MP), 0.4 (fraction of Fe in Fe2O3)
Fe3O4: -1.659571429 (exp), -1.84 (theo_MP), 0.180428571 (exp-theo_MP), 0.428571429 (fraction of Fe in Fe3O4)
FeO: -1.4097 (exp), -1.669 (theo_MP), 0.2593 (exp-theo_MP), 0.5 (fraction of Fe in FeO)
All energies are in eV/atom. Then I have used Linear-trendline to get the slope (by fixing intercept= 0). But I am not getting -2.27 or -2.733. The slope I am getting is 0.446!!
Can you please tell where I am doing the mistake?