Just to add that the attached files are for AFM.
On Fri, 11 Dec 2015, t...@theochem.tuwien.ac.at wrote:
With strongly correlated solids, it is usually possible to
stabilize several electronic configurations. For FeO, if
you start a mBJ or LDA+U calculation from the PBE density,
then a metallic state is obtained. The state with a gap, which
is more stable, can be obtained by running first a constrained
LDA+U calculation with -orbc:
1) change manually the occupation (that you need to know) in
case.dmatup/dn of a LDA+U calculation,
2) execute "x orb -up/dn" to generate case.vorbup/dn
3) run LDA+U with -orbc instead of -orb
4) save the contrained calculation when it is finished
4) run LDA+U or mBJ as usual.
The struct and dmat files of a recent LDA+U calculation on FeO are
attached.
F. Tran
On Thu, 10 Dec 2015, John McLeod wrote:
Hello all,
I tried to calculate the electronic structure of FeO using mBJ.
1. I took the cubic FeO structure, made a 2x2x2 primitive supercell,
relabeled the Fe sites "1" and "2" to get the appropriate AFM ordering, ran
sgroup, and obtained a rhombohedral cell with 2 Fe sites and 1 O site. This
structure looks correct when viewed with VESTA or xcrysden, so I think I am
using the correct structure.
2. I run a spin-polarized PBE calculation, initializing the Fe to "up" and
"down", and the O to "no spin", this converges quickly and obtains a zero
band gap as expected.
3. I run an mBJ calculation using PRATT mixing, slowly increasing the
mixing factor. The energy converges in 20 cycles or so, however the charge
never converges - it keeps "sloshing" back and forth between the two Fe
sites. The band gap for this system remains at zero.
In PRL 102 226401 (2009) and mBJ calculation on FeO reports a gap of 1.82
eV. May I ask Dr. Fabian Tran and/or Dr. Peter Blaha, to obtain these
results did you:
1. Perform an AFM calculation or just a spin-polarized calculation?
2. Perform any sort of structural optimization?
3. Use PRATT mixing only, or switch back to MSR1?
I also tried this approach with hematite (Fe2O3), obtaining a rhombohedral
structure with 4 inequivalent Fe sites (as expected), and following the
same steps I obtained good charge and energy convergence in mBJ as well as
a reasonably accurate band gap - so I find it a bit curious that my
approach fails for FeO.
I would greatly appreciate a quick tip on how the original calculations in
PRL 102 226401 were performed.
Regards,
John McLeod
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