[Pw_forum] DFT+U: about how to get U

[Chao Cao]

Dear Matteo,
  Just out of curiosity, I tried to calculate U parameter for
2p-electron of oxygen in a NiO cluster following the procedure you
suggested. Before the calculation, I was guessing that the out for
oxygen would be very small, however... it turned out to be ~6 eV for Ni
(which I guess is still reasonable) and ~11 eV for O... So I guess
either my procedure was wrong or there was something fundamentally wrong
so that practically I should not try to calculate U for 2p electrons? I
am really newbie in this LDA+U thing, sorry about these naive questions...

And this is the input file, and for perturbation calculations I just
change Hubbard_alpha value and put "diago_thr_init = 1.0d-12",
"startingwfc='file' " and "startingpot='file' "s in there.

Thanks a lot

&control
  calculation = 'scf'
  restart_mode = 'from_scratch'
  prefix = 'test'
  outdir = './'
/
&system
  ibrav = 0, celldm(1) = 1.88972687777, nat = 8, ntyp = 2, ecutwfc = 40,
ecutrho = 400
  occupations = 'tetrahedra'
  nspin = 2, multiplicity = 9
  lda_plus_u = .true.,
  Hubbard_alpha(1) = 0.00
  Hubbard_U(1) = 1.0d-20,
  Hubbard_U(2) = 1.0d-20,
/
&electrons
  mixing_beta = 0.2
  conv_thr = 1.0d-8
/
ATOMIC_SPECIES
Ni  58.6934  Ni.pbe-van_bm.UPF
O   15.9994  O.pbe-van_bm.UPF
ATOMIC_POSITIONS alat
Ni       1.044490324   1.227039735   1.098575578
Ni       1.227039735  -1.044490324  -1.098575578
Ni      -1.044490324  -1.227039735   1.098575578
Ni      -1.227039735   1.044490324  -1.098575578
O       -0.830714207  -1.049403843  -0.960644686
O       -1.049403843   0.830714207   0.960644686
O        0.830714207   1.049403843  -0.960644686
O        1.049403843  -0.830714207   0.960644686
K_POINTS automatic
  1,1,1,0,0,0
CELL_PARAMETERS
  14.000000000   0.000000000   0.000000000
   0.000000000  14.000000000   0.000000000
   0.000000000   0.000000000  14.000000000


Chao Cao

Matteo Cococcioni wrote:
>
> Dear Chao Cao,
>
> Chao Cao wrote:
>> Dear Matteo,
>>  Thanks for this fast response. I have two more questions.
>> I am assuming that by "non-equivalent" you mean non-equivalent site
>> instead of non-equivalent type, i.e. if I have two Fe atoms within 1
>> unit cell, I'll have to treat them individually, therefore they might
>> have different U number?
>>
>>   
>
> Yes, I meant non equivalent sites. two atoms of the same kind but on
> non-equivalent sites may have different U.
>
>> Also, it looks to me that this method is not restricted to d-electrons,
>> and practically it also applies to p and f electrons, am I right?
>>
>>   
>
> formally it's possible to apply it to p or s electrons. however  the
> LDA+U was designed for localized orbitals.
> also with extended orbitals you may need to orthogonalize them because
> you may have significant overlaps bewteen different atoms.
> no problem with f states.
>
> Matteo
>
>> Chao Cao
>>
>> Matteo Cococcioni wrote:
>>  
>>> Dear Chao Cao,
>>>
>>> the linear response procedure is repeated only for non-equivalent
>>> Hubbard atoms.
>>>
>>> Regards,
>>>
>>> Matteo
>>>
>>>
>>> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>>> Matteo Cococcioni
>>> Department of Chemical Engineering and Materials Science
>>> University of Minnesota
>>> 151 Amundson Hall
>>> 421 Washington Av. SE
>>> Minneapolis, MN 55455
>>> Tel. +1 612 624 9056    Fax +1 612 626 7246
>>> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>>>
>>>
>>> On Oct 16, 2007, at 3:02 PM, Chao Cao wrote:
>>>
>>>    
>>>> Hi there,
>>>>   I read about M. Cococcioni's paper and thesis on how to get the U
>>>> parameter, and have the following question on mind:
>>>>   Does the procedure of perturbing atomic occupation go through every
>>>> single atom or just "hubbard" atoms? In the latter case, does the
>>>> response matrix chi include elements related with hubbard atoms only (
>>>> i.e. chi(m,n) m and n are both hubbard atoms ), or it has to include
>>>> everything? If it includes everything, what do we do about elements
>>>> related to non-hubbard atoms (maybe set them to 0 (?))?
>>>>
>>>>   Thanks in advance.
>>>>
>>>> Chao Cao
>>>>
>>>> -- 
>>>> Chao Cao
>>>>
>>>> Quantum Theory Project and Department of Physics
>>>> University of Florida, Gainesville, FL 32611
>>>> U.S.A.
>>>>
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>>   
>
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-- 
Chao Cao

Quantum Theory Project and Department of Physics
University of Florida, Gainesville, FL 32611
U.S.A.