[Wien] Problems with FM+U+SOC with natorb=1 nlorb=2

[Peter Blaha]

I do NOT officially support 2 l values / atom for GGA+U. It may/may not 
work in various programs.

The reason is simply, that in WIEN2k the U is applied only inside the 
sphere and the V_orb potential is calculated from the occupations of an 
orbital, varying from 0 to 1.
I.e. if n=1 (an orbital is fully occupied), it gets a potential which 
shifts this state by U/2 down, on the other hand, if a particular 
orbital is empty, it will be shifted up by U/2.

The problems come with relatively "delocalized" orbitals like the 5d 
states of a 4f element.

Check out the "fractional charge" within the sphere as printed in 
case.outputst.
   4F*     -0.590624     -0.590624  2.50  2.50    0.9844  F
   5D*     -0.208649     -0.208649  0.50  0.50    0.4864  F

You can find that Sm-4f is nearly completely confined in the sphere 
(0.9844) and applicationsof U is "well defined", but one 5d electron has 
less than 0.5 e inside the sphere !!!
Depending on the rare earth and on RMT it means that even a fully 
occupied 5d state does NOT get shifted down due to GGA+U, but basically 
all d-orbitals will be shifted up.



Am 24.07.2020 um 18:03 schrieb pluto:
> Dear All,
> 
> I am trying to calculate a simple 4f compound with GGA+U, ferromagnetic 
> exchange (FM) and SOC. FM calculation without SOC using the literature U 
> settings looks reasonable, I am getting a gapped band structure similar 
> to anyone else.
> 
> But running SCF with GGA+U and SOC removes the gap, it also seems to 
> change the exchange splitting of 4f, which basically tells me that U on 
> 4f is not in effect anymore. Actually the problem happens with this 
> inorb file, when natorb=1 and nlorb=2:
> 
>    1  1  0                     nmod, natorb, ipr
> PRATT  1.0                    BROYD/PRATT, mixing
>    1 2 2 3                          iatom nlorb, lorb
>    1                              nsic 0..AMF, 1..SIC, 2..HFM
>     0.25 0.00        U J           U on d levels
>     0.42 0.00        U J           U on f levels
> 
> When nlorb is reduced to 1, and U is used only for 4f levels things 
> start to look "normal" also with SOC. So, it seems SOC cannot handle 
> nlorb>1 (perhaps just a bug).
> 
> I am using couple of years old version of WIEN2k, perhaps this has been 
> fixed in the meantime. Otherwise, any comment would be appreciated!
> 
> Best,
> Lukasz
> 

-- 
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
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