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

Bramha Pandey pandey.bramha at gmail.com
Sun Oct 7 19:00:18 CEST 2012

```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
> > Ph.D Student Indian School of Mines(ISM)
> >
> >
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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
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Thanks and Regards