[Pw_forum] about U value determination in DFT+U calculation

[Gabriele Sclauzero]

On 07/20/2010 11:24 AM, Gabriele Sclauzero wrote:
> Dear Jia Chen,
>
>    do you really need to use this specific pseudopotential? It looks 
> like it was built for specific purposes (XPS calculations) and has 
> some non-standard features (in my opinion at least). Specifically, it 
> has more wavefunctions than beta projectors and moreover the 3d 
> channel is treated as local (I don't if and how this may affect 
> transferability).
> However the 3D wavefunction is present and has occupation greater than 
> zero (contrary to the 4D wfc), so I can't see the reason why the code 
> should give such result. 

Actually I realized that the subroutine checks if the occupation is 
greater OR equal to zero, so that in your case the 4D wavefunction is 
actually selected, because it is listed after the 3D.

You can solve this problem by changing the following line (in 
offset_atom_wfc.f90)
    IF ( upf(nt)%lchi(n) == Hubbard_l(nt) ) offset(na) = counter
into
    IF ( upf(nt)%oc(n) > 0.D0 .AND. upf(nt)%lchi(n) == Hubbard_l(nt) ) 
offset(na) = counter

I don't know if this fix does fit the general logic of DFT+U and 
deserves to be included permanently in the code: maybe it does, since in 
most cases one puts the +U correction to (partly) occupied electronic 
manifolds. At least so far I haven't seen anyone applying it to empty 
shells... does anyone have a clue/hint about that?

GS


> I will have a look at it, but in the meanwhile I suggest you to try 
> also one of the other PBE  PPs for Co which are present on the QE website.
>
>
> GS
>
> On 07/19/2010 11:13 PM, jia chen wrote:
>> Dear Gabriele Sclauzero,
>>
>> Thank you so much for your help. I did an atomic calculation 
>> according to your suggestion using that pseudo-potential. Sadly, the 
>> occupation number is not correct.
>> first step
>> atom    1   Tr[ns(na)]=   7.0000000
>> and after optimization
>> atom    1   Tr[ns(na)]=   0.0748899
>>
>> The pseudo-potential I got from website of QE named 
>> Co.pbe-sp-mt_gipaw.UPF 
>> <http://www.pwscf.org/pseudo/1.3/UPF/Co.pbe-sp-mt_gipaw.UPF>
>> and header of this pseudo-potential is copied below
>> <PP_HEADER>
>>     0                   Version Number
>>    Co                   Element
>>     NC                  Norm - Conserving pseudopotential
>>      F                  Nonlinear Core Correction
>>   SLA  PW   PBX  PBC    PBE  Exchange-Correlation functional
>>     17.00000000000      Z valence
>>   -287.58146877626      Total energy
>>        0.000      0.000 Suggested cutoff for wfc and rho
>>      2                  Max angular momentum component
>>   1193                  Number of points in mesh
>>      6    2             Number of Wavefunctions, Number of Projectors
>>   Wavefunctions         nl  l   occ
>>                         3S  0  2.00
>>                         4S  0  0.00
>>                         3P  1  6.00
>>                         4P  1  0.00
>>                         3D  2  7.00
>>                         4D  2  0.00
>> </PP_HEADER>
>>    
>> According to your post, I don't think it can be any problem, but 
>> atomic calculation I did is not correct. Can you give me further help 
>> about what can go wrong? I looked inside offset_atom_wfc.f90, but I 
>> have no idea how to check if pw picks right atomic wavefunction.... 
>> Can you give me some hints about that? Thank you so much!
>>
>> Bests
>> -- 
>> Jia Chen
>>
>> Dept of Chemistry
>> Princeton University
>> Princeton, NJ 08544
>>
>>
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>>    
>
>
> -- 
>
> Gabriele Sclauzero, EPFL SB ITP CSEA
> PH H2 462, Station 3, CH-1015 Lausanne
>    
>
>
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-- 

Gabriele Sclauzero, EPFL SB ITP CSEA
PH H2 462, Station 3, CH-1015 Lausanne

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