[Wannier] Eq. (B1) not satisfied in kmesh_get (1)
Jonathan Yates
jonathan.yates at materials.ox.ac.uk
Fri Nov 19 01:14:38 CET 2010
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
--
Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK
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