<div dir="ltr">Thank you ,Dr Yates .<br>I read wann_phases, and didnot notice the control<br>tag on these two quantities.<br><br><br>Best,<br>Hai-Ping<br><br><div class="gmail_quote">On Wed, Sep 17, 2008 at 11:23 PM, Jonathan Yates <span dir="ltr"><<a href="mailto:jry20@cam.ac.uk">jry20@cam.ac.uk</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div class="Ih2E3d">On Tue, 16 Sep 2008, lan haiping wrote:<br>
<br>
> I read several lines of wannier routines ,and try to understand several<br>
> key<br>
> points formulated in the paper and programme.<br>
> My question is about wannier center formulated in wannier90. In the MV<br>
> paper,<br>
> \bar{r}_n = -\frac{1}{N} \Sum_{k,b} w_b b Im lnM_{n,n}^{k,b}, while<br>
> wan_omega<br>
> subroutine formulates this equation with 2 quantities: sheet and csheet.<br>
> I donot catch this point ,and donot know the meaning of this 2 quantities.<br>
> Would you please explain some details in this point ?<br>
<br>
</div> Unless you use the guiding centres option, csheet=1.0 and sheet=0.0 and<br>
the formula in wann_omega reduces to the equation you reproduce above.<br>
<br>
In the above formula (and that for Omega_D) there appears the log of<br>
M_mn, ie the log of a complex number. This introduces a possible ambiguity<br>
(ie different branch cuts - see section IV.D.2 of MV). In many cases this<br>
causes no problems, but in certain systems it does cause problems in the<br>
minimisation - typically one gets a few or many WF with very large spread,<br>
and the value of Omega_D is large. One solution is to use the<br>
guiding_centres option.<br>
You will find more details in the wann_phases subroutine - here csheet<br>
and sheet are computed. These are then used control the choice of branch<br>
cut in wann_omega.<br>
<br>
Jonathan<br>
<br>
<br>
--<br>
Dr Jonathan Yates | Theory of Condensed Matter Group<br>
Corpus Christi College | Cavendish Laboratory<br>
Cambridge, CB2 1RH, UK | Cambridge, CB3 OHE, UK<br>
email <a href="mailto:jry20@cam.ac.uk">jry20@cam.ac.uk</a> | Tel +44 (0)1223 337461<br>
<br>
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</blockquote></div><br><br clear="all"><br>-- <br>Hai-Ping Lan <br>Department of Electronics ,<br>Peking University , Bejing, 100871<br><a href="mailto:lanhaiping@gmail.com">lanhaiping@gmail.com</a>, <a href="mailto:hplan@pku.edu.cn">hplan@pku.edu.cn</a><br>
</div>