[Pw_forum] U for Oxygen

[Matteo Cococcioni]

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>/* wrote:
>
>
>     From: Matteo Cococcioni <matteo at umn.edu>
>     Subject: Re: [Pw_forum] occupation
>     To: "PWSCF Forum" <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
>
>
>


-- 
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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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