[Wannier] Question about wannier center !

[lan haiping]

Dear All,

  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 ?
Thank you!

-- 
Hai-Ping Lan
Department of Electronics ,
Peking University , Bejing, 100871
lanhaiping at gmail.com, hplan at pku.edu.cn
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