[Wien] mBJ for FeO

[tran at theochem.tuwien.ac.at]

Just to add that the attached files are for AFM.

On Fri, 11 Dec 2015, tran at 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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