[Pw_forum] U for Oxygen

Matteo Cococcioni matteo at umn.edu
Thu Aug 6 17:15:09 CEST 2009


Dear Ali

ali kazempour wrote:
> Dear Matteo
> In your tutorial about LDA_U, you mentioned that the perturbation 
> should be isolated. and  said that we normally use supercell of 
> increasing size up to when convergence of is reached. I don't 
> understand how do you increase the size of the cell and how do you 
> compute the U in larger supercell.? I mean how do you apply 
> perturbation to bigger size or how to extrapolate the U to converge?
>

just like to the small one. please run the examples in the tutorial

> Another question according to prior email for computation of U by 
> common method(not linear response) is : you mentioned that espresso 
> cann't directly change the occupation of special orbital by hand, but 
> it is possible to do by using constraint on total number of 
> electron(total occupation) indirectly . Do you mean that( for example 
> for Ti atom that has 2 electron in d orbital) ,what can i do is change 
> the of number of nelup and neldw  without change in nelec? or I have 
> to do another switch? Would you please tell me in more details.
> Thank you very much for your aids
> Ali Kazempour
> Physics department, Isfahan University of Technology
> 84156 Isfahan, Iran. Tel-1: +98 311 391 3733
> Fax: +98 311 391 2376 Tel-2: +98 311 391 2375
>
> --- On *Tue, 8/4/09, Matteo Cococcioni /<matteo at umn.edu>/* wrote:
>
>
>     From: Matteo Cococcioni <matteo at umn.edu>
>     Subject: Re: [Pw_forum] U for Oxygen
>     To: "PWSCF Forum" <pw_forum at pwscf.org>
>     Date: Tuesday, August 4, 2009, 9:52 AM
>
>
>     this is what comes out from the calculation (U(O) > U(Ni)).
>     whether it's
>     reasonable to apply U on O or not, I'm not sure.
>
>     I think the U shouldn't be used on states that are completely
>     occupied.
>
>     Matteo
>
>
>
>     ali kazempour wrote:
>     > Dear Matteo
>     > This means that hubbard parameter for oxygen is large (grater than
>     > Ni). Is it correct or originate from another challenge?
>     > thanks
>     >
>     > Ali Kazempour
>     > Physics department, Isfahan University of Technology
>     > 84156 Isfahan, Iran. Tel-1: +98 311 391 3733
>     > Fax: +98 311 391 2376 Tel-2: +98 311 391 2375
>     >
>     > --- On *Tue, 8/4/09, Matteo Cococcioni /<matteo at umn.edu
>     </mc/compose?to=matteo at umn.edu>>/* wrote:
>     >
>     >
>     >     From: Matteo Cococcioni <matteo at umn.edu
>     </mc/compose?to=matteo at umn.edu>>
>     >     Subject: Re: [Pw_forum] U for Oxygen
>     >     To: "PWSCF Forum" <pw_forum at pwscf.org
>     </mc/compose?to=pw_forum at pwscf.org>>
>     >     Date: Tuesday, August 4, 2009, 6:59 AM
>     >
>     >
>     >
>     >     Dear Ali,
>     >
>     >
>     >
>     >     ali kazempour wrote:
>     >     > Dear Matteo
>     >     > I used your comment and followed   your example for NiO and I
>     >     succeed
>     >     > to get U for TiO2. But in file Ur16.out I see three column .
>     >     >
>     >
>     >     I don't have any three column section in any of my files. so if
>     >     you want
>     >     me to help you you have to report at least a section of your
>     output
>     >     file. This is a good habit actually in consideration of the
>     fact that
>     >     this is not a private conversation (I would have asked you
>     in any
>     >     case
>     >     as I don't remember by heart the format of any file) between me
>     >     and you
>     >     but a message to the forum and you want other people to
>     understand
>     >     what you are saying.
>     >
>     >     > The first is number of atom in supercell , second is U
>     value for Ni
>     >     > atom and I don,t know  the third? does the third belong
>     to  U value
>     >     > for Oxygen or not? Because the third column kas big value?
>     >     >
>     >     >
>     >     > another question is for isolated atom Hubbard parameter.
>     What do
>     >     you
>     >     > expect about the value of U for Isolated atom? Is this big
>     value
>     >     > (greater than 10 eV) or  it would be tiny value?
>     >     >
>     >
>     >     I think it will be meaningless for the reasons I explained
>     in my last
>     >     email. To obtain a meaningful number for the isolated atom you
>     >     probably
>     >     have to abandon the idea to use a perturbation in the
>     potential and
>     >     change instead the number of electrons directly. This means
>     you will
>     >     have to do calculations on atoms having fractional charges which
>     >     requires additional corrections if you use a code designed for
>     >     periodic
>     >     systems (crystals). However I have never done this isolated atom
>     >     calculation of U before so I don't have more details about it.
>     >     I see (from a private email) you are thinking of computing U
>     for the
>     >     isolated atom and to obtain a value for the crystal just by
>     >     dividing by
>     >     the epsilon_inft. the method is proposed in
>     >
>     >     http://link.aps.org/doi/10.1103/PhysRevB.74.045202
>     >
>     >     (which I haven't re-read yet).
>     >
>     >     I see a couple of problems:
>     >
>     >     1) (not important for ZnO). suppose you have Fe3O4 with Fe2+ and
>     >     Fe3+.
>     >     these Fe ions likely have different U. how do you obtain
>     >     a different number from the atomic code? would you do the
>     calculation
>     >     for isolated Fe2+ and Fe3+?
>     >
>     >     2) how do you get epsilon? since it's a linear response
>     property I
>     >     don't
>     >     think its calculation is any cheaper than the direct
>     calculation of U.
>     >
>     >     regards,
>     >
>     >     Matteo
>     >
>     >     > should we choose for running the script for isolated atom only
>     >     gamma
>     >     > point or we have to choose a fine mesh?
>     >     > thanks a lot
>     >     >
>     >     >
>     >     > Ali Kazempour
>     >     > Physics department, Isfahan University of Technology
>     >     > 84156 Isfahan, Iran. Tel-1: +98 311 391 3733
>     >     > Fax: +98 311 391 2376 Tel-2: +98 311 391 2375
>     >     >
>     >     > --- On *Sun, 8/2/09, Matteo Cococcioni /<matteo at umn.edu
>     </mc/compose?to=matteo at umn.edu>
>     >     </mc/compose?to=matteo at umn.edu
>     </mc/compose?to=matteo at umn.edu>>>/* wrote:
>     >     >
>     >     >
>     >     >     From: Matteo Cococcioni <matteo at umn.edu
>     </mc/compose?to=matteo at umn.edu>
>     >     </mc/compose?to=matteo at umn.edu </mc/compose?to=matteo at umn.edu>>>
>     >     >     Subject: Re: [Pw_forum] occupation
>     >     >     To: "PWSCF Forum" <pw_forum at pwscf.org
>     </mc/compose?to=pw_forum at pwscf.org>
>     >     </mc/compose?to=pw_forum at pwscf.org
>     </mc/compose?to=pw_forum at pwscf.org>>>
>     >     >     Date: Sunday, August 2, 2009, 8:31 AM
>     >     >
>     >     >
>     >     >     Dear Ali,
>     >     >
>     >     >     1, -1, 0 are just spin indexes to tell the code what
>     is the
>     >     relative
>     >     >     magnetization of the atoms (parallel, antiparallel, or
>     none). if
>     >     >     your system is non magnetic put all 0. or set magn =
>     .false.
>     >     and put
>     >     >     nothing.
>     >     >     you should look at the examples on Fe and Si as well and
>     >     learn from
>     >     >     there by comparison.
>     >     >
>     >     >     Matteo
>     >     >
>     >     >
>     >     >
>     >
>     >
>     >     --
>     >     %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>     >     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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>     >
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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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-- 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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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