[Wannier] Eq. (B1) not satisfied in kmesh_get (1)

[Jonathan Yates]

On 18 Nov 2010, at 23:47, Jian-Xin Zhu wrote:
> One remark: The above listed k-values are generated from the wien2wannier interface. 
> I have a strange observation. For the number of k-points of like 6  6  6 (a fcc structure), the error is encountered. 
> For the number of k-points like 8  8  8, the error does not appear. However, if I use even larger number of k-points, 
> e.g., 12 12  12, the error comes up again. It seems there is no guarantee  to resolve the problem by increasing the 
> number of k-points (Of course, the calculation also becomes more expensive with large number of k-points). 

There is simple explanation:
 1/8 can be exactly represented with 3decimal places of precision. 1/6 and 1/12 cannot be precisely expressed with a finite number of decimal places.
So the fact that you see the error with grids of size 6 and 12 but not 8 shows us that it is a precision error.

 So either you increase the precision of the kpoints. Or decrease the value of kmesh_tol. They will both achieve the same end.

Jonathan





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