[Pw_forum] very large value 'U' obtained for 'GaAs' by linear response method

[Burak Himmetoglu]

Dear Brahma,

Ga has a full d-shell. Therefore, if you try to perturb the d-shell of Ga,
you can reduce the number of electrons localized on d-states by a positive
Hubbard_alpha but there is no way to increase their occupations with a
negative Hubbard_alpha. Therefore, the response matrices will be non-linear
and you will get very small numbers in them. When you invert these
matrices, very large numbers will appear.

Calculating U for full d-shells is not easy, and there is no simple
solution (Another known example is ZnO). My personal opinion is that the
use of LDA+U is questionable for filled d-shells. In fact if you check the
paper mentioned by Matteo, the gap for GaAs is corrected by applying U and
V (inter-site interactions) on Ga-p states and states which overlap with
Ga-p. No correction on Ga-d is applied.

Best regards,

Burak

On Sun, Oct 7, 2012 at 12:02 PM, Bramha Pandey <pandey.bramha at gmail.com>wrote:

> sorry for wrong matrix copied in previous mail.
>
> CHI0^-1 - CHI^-1 Matrix
>
>     0.0000    0.0000    0.0000
>     0.0000    0.0000    0.0000
>
>     0.0000    0.0000    0.0000
>   type:            1  U0 =   0.000000000000000E+000
>
> On Sun, Oct 7, 2012 at 10:30 PM, Bramha Pandey <pandey.bramha at gmail.com>wrote:
>
>> Dear Prof. Matteo,
>> i am using Ga, pseudo with 3d as a valence, Hubbard_l=2 is set for 'Ga'.
>> If it should change how much value i have to set it?
>>
>> Dear sir i am totally struck by zero matrix element in ch0^-1 - chi^-1,
>> so always it gifted me ZERO value where as ch0 and chi matrix are NON ZERO
>> with same element value.
>> CHI_0 Matrix
>>    -0.0002  -0.0002   0.0005
>>   -0.0002  -0.0002   0.0005
>>    0.0005   0.0005  -0.0010
>>    CHI Matrix
>>    -0.0002  -0.0002   0.0005
>>   -0.0002  -0.0002   0.0005
>>    0.0005   0.0005  -0.0010
>>
>>   CHI0^-1 - CHI^-1 Matrix
>>
>>     0.0000    0.0000
>>     0.0000    0.0000
>>   type:            1  U0 =   0.000000000000000E+000
>> This above is for all the  2 atoms supercell combination when we take the
>> ZB structure with 2 atoms: (1) when both atoms are 'Ga'
>> (2) when both atoms are 'Ga1' and 'Ga' (3) when both atoms are different
>> 'Ga' and 'As'.
>>
>> All above three conditions are tested under one atom(Ga1 or Ga) is
>> perturbed.
>> Please Sir give me some ray of hope so that i can get rid of this
>> situation.
>>
>>
>> On Sun, Oct 7, 2012 at 8:10 PM, Matteo Cococcioni <matteo at umn.edu> wrote:
>>
>>> Dear Bramha,
>>>
>>> in J. Phys.: Condens. Matter 22 (2010) 055602 we did a similar
>>> calculation but we got pretty different numbers (see Table 2 of the
>>> reference). Maybe the states of Ga you applied U or alpha to are
>>> completely full. what is the value of l set for Ga in set_hubbard_l ?
>>> did you change that? also, for Ga, you better use a pseudo with 3d
>>> states in the valence rather than frozen in the core.
>>>
>>> Matteo
>>>
>>>
>>>
>>> On Sun, Oct 7, 2012 at 7:31 AM, Bramha Pandey <pandey.bramha at gmail.com>
>>> wrote:
>>> > First of all thank you very much Dear Prof.Stefano.
>>> > I have change the input as ZB 'GaAs' structure and calculate the 'U'
>>> value
>>> > for both 'Ga' and 'As' which is given bellow.
>>> > But i wondered to see the 'U' value of 'Ga' 1010.79 which is quite
>>> large so
>>> > how can i figure out this is  correct or wrong?
>>> > No of Atom        U_Ga                       U_As
>>> > 2                1043.35792360332    2.87817590827985
>>> > 16              1010.81003743078    2.82970777976411
>>> > 54              1010.79529573193    2.82968584264055
>>> > 128             1010.79528904780    2.82968583269392
>>> > 250             1010.79528904476    2.82968583268940
>>> > Any comment is welcome.
>>> > --
>>> > Thanks and Regards
>>> > Bramha Prasad Pandey
>>> > Ph.D Student Indian School of Mines(ISM)
>>> > Dhanbad, INDIA.
>>> >
>>> >
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>>>
>>>
>>>
>>> --
>>> Matteo Cococcioni
>>> Department of Chemical Engineering and Materials Science,
>>> University of Minnesota
>>> 421 Washington Av. SE
>>> Minneapolis, MN 55455
>>> Tel. +1 612 624 9056    Fax +1 612 626 7246
>>> _______________________________________________
>>> Pw_forum mailing list
>>> Pw_forum at pwscf.org
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>>>
>>
>>
>>
>> --
>> Thanks and Regards
>> Bramha Prasad Pandey
>> Ph.D Student Indian School of Mines(ISM)
>> Dhanbad, INDIA.
>>
>>
>
>
> --
> Thanks and Regards
> Bramha Prasad Pandey
> Ph.D Student Indian School of Mines(ISM)
> Dhanbad, INDIA.
>
>
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