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Dear all,
I'm frustrated with the formation energy calculation in supercell Fe31CrC (or Fe31NiC). Hope you can give me some hint on it.
I First construct a 2*2*2 fcc Fe, which is supercell Fe32, Then I substituted one Fe atom with one Cr (or Ni) atom, also put one Carbon atom in one of the O site of the supercell. Then we got the supercell Fe31CrC (or Fe31NiC).
According to my understanding, the definition of formation energies is the total energy difference between compound and constituent elements in the solid state. So the formation energy of the supercell Fe31CrC is:
Ef(Fe31CrC) = Et(Fe31CrC)-31Et(Fe)-Et(Cr)-Et(C)
Et is the total energy of the supercell and the corresponding bulk Fe, bulk Cr, bulk C.
My question is:
1) if we do the calculation spin polarized, what is the reference state of bulk Fe, bulk Cr, bulk Ni, and bulk C? (should it be FM bcc Fe, graphite C, bcc FM Cr, fcc FM Ni ?)
2) if we do the calculation nonmagnetic, then what is the reference state of bulk Fe, bulk Cr, bulk Ni and bulk C?

Thanks a lot! Have a nice weekend! Any comments are welcomed!

you always have to take the bulk ground states of the constituents (i.e: bcc FM Fe, fcc FM Ni, graphite C, ...

got it! Thanks a lot! Have a nice day!