[Wannier] Question about wannier center !

[lan haiping]

Thank you ,Dr Yates .
I  read wann_phases, and  didnot notice the control
tag on these two quantities.


Best,
Hai-Ping

On Wed, Sep 17, 2008 at 11:23 PM, Jonathan Yates <jry20 at cam.ac.uk> wrote:

> On Tue, 16 Sep 2008, lan haiping wrote:
>
> >  I read several lines of wannier routines ,and try to understand several
> > key
> > points formulated in the paper and programme.
> >  My question is about wannier center formulated in wannier90. In the MV
> > paper,
> > \bar{r}_n = -\frac{1}{N} \Sum_{k,b} w_b b Im lnM_{n,n}^{k,b}, while
> > wan_omega
> > subroutine formulates this equation with 2  quantities: sheet and csheet.
> > I donot catch this point ,and donot know the meaning of this 2
> quantities.
> > Would you please explain some details in this  point ?
>
>   Unless you use the guiding centres option, csheet=1.0 and sheet=0.0 and
> the formula in wann_omega reduces to the equation you reproduce above.
>
>  In the above formula (and that for Omega_D) there appears the log of
> M_mn, ie the log of a complex number. This introduces a possible ambiguity
> (ie different branch cuts - see section IV.D.2 of MV). In many cases this
> causes no problems, but in certain systems it does cause problems in the
> minimisation - typically one gets a few or many WF with very large spread,
> and the value of Omega_D is large. One solution is to use the
> guiding_centres option.
>  You will find more details in the wann_phases subroutine - here csheet
> and sheet are computed. These are then used control the choice of branch
> cut in wann_omega.
>
>  Jonathan
>
>
> --
> Dr Jonathan Yates         |    Theory of Condensed Matter Group
> Corpus Christi College    |    Cavendish Laboratory
> Cambridge, CB2 1RH, UK    |    Cambridge, CB3 OHE, UK
> email jry20 at cam.ac.uk     |    Tel +44 (0)1223 337461
>
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-- 
Hai-Ping Lan
Department of Electronics ,
Peking University , Bejing, 100871
lanhaiping at gmail.com, hplan at pku.edu.cn
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