What is DZP-DZP for Fe, and DZP-DZ for C????
Yes, BSSE will always reduce the binding energy (cohesion energy,
solvation enthalpy, etc.) since without ghosts, the total energy will
always be higher than with ghosts.
I would say that ghosts around C would be more important than in Fe,
since Fe cluster has more degrees of freedom due to many atoms coupled
close enough.
So your approach is perfectly fine.
Did you try to do spin-polarized calculations? (Although, normally they
should lower even more the solution enthalpy).
One more thing, as far as I understand, you haven't taken BSSE in your
Fe and graphite vacancy formation energies, and cohesion energies. Thus
you are making the error there as well, so your agreement with
literature might be not that good.
