Thank You very much Dear Prof. Burak, Prof Giuseppe and Dear Prof. Matteo for giving such a explanation for my problem. Thank you very much once again to all my DEAR eminent Prof. for your kind attention and help.
On Mon, Oct 8, 2012 at 2:54 PM, Giuseppe Mattioli < giuseppe.mattioli at ism.cnr.it> wrote: > > > Dear all > > Burak has indeed described well the problem, but something more can be > said: the Ga 3d shell (as well as the Zn 3d shell in ZnO) is almost > atomic-like and give rise to a very narrow band in III-V > semiconductors, horribly affected by delocalisation (aka > self-interaction) problems. This band is raised in energy far more > than the As (3p) valence band; so the two bands are mixed (and they > should not) and the valence band maximum is pushed up towards the > conduction band minimum. Moreover, you cannot extract meaningful > self-consistent U values by linear response procedures in the limit of > a simplified "on-site, one-shell" approach. However, it is not > forbidden to use "semi-empirical" U values, as long as you have a good > knowledge of the physics of your system... The above problems in DFT > calculations of GaAs and ZnO are addressed in a Zunger paper, very > long and quite... difficult to flick through. > > Lany, S. and Zunger, A.; Phys. Rev. B 78, 235104 ͑(2008͒). > > In a short, you may try to decouple the Ga (3d) band from the As (3p) > band by hammering with some empirical U value the head of the Ga 3d > band. And you can recover a very good band gap value by pushing down > (more softly...) the As 3p band. You may test your results against a > hybrid functional. I've done it in the case of ZnO, and I've obtained > quite good results. > > Matteo suggest that the Ga 3d has to be included in the calculation. > In my experience (but I'm the "empirical" kind of computational > guy...) The Ga 3d shell is mandatory in the case of GaN if you want a > good lattice parameter. In the case of GaAs you can obtain good > results (band gap included) by embedding the Ga 3d electrons within > the Ga pseudopotential, and by using a NLCC approach. > This leads to some kind of decoupling of the Ga 3d and As 3p bands. I > remember some old papers (2000-2005) by Van de Walle and Neugebauer on > GaN in which a Ga PP without 3d shell was used after a lattice > parameter optimisation performed by using a Ga PP with 3d shell. > > HTH > > Giuseppe > > Quoting Burak Himmetoglu <himm0013 at umn.edu>: > > > 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. > >>>> > > >>>> > > >>>> > _______________________________________________ > >>>> > Pw_forum mailing list > >>>> > Pw_forum at pwscf.org > >>>> > http://pwscf.org/mailman/listinfo/pw_forum > >>>> > >>>> > >>>> > >>>> -- > >>>> 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 > >>>> http://pwscf.org/mailman/listinfo/pw_forum > >>>> > >>> > >>> > >>> > >>> -- > >>> 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. > >> > >> > >> _______________________________________________ > >> Pw_forum mailing list > >> Pw_forum at pwscf.org > >> http://pwscf.org/mailman/listinfo/pw_forum > >> > > > > Giuseppe Mattioli > ISM-CNR > Italy > > > > > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > -- Thanks and Regards Bramha Prasad Pandey Ph.D Student Indian School of Mines(ISM) Dhanbad, INDIA. -------------- next part -------------- An HTML attachment was scrubbed... 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