[Wien] mBJ for FeO

[John McLeod]

Thanks for the help!

-John

On 15-12-11 03:53 AM, tran at theochem.tuwien.ac.at wrote:
> 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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>>
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