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

[Jian-Xin Zhu]

Dear Jonathan,

If it goes this way, I may avoid the error by using rational fractions  
in all three directions, like 1/20  1/20  1/10 (if allowed for a  
specific crystal structure).
Does it make sense?

Thanks,

Jianxin


On Nov 18, 2010, at 5:14 PM, Jonathan Yates wrote:

>
> 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
> tel: +44 (0)1865 612797                http://users.ox.ac.uk/ 
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>
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Jian-Xin Zhu, Ph.D
Theorertical Division, MS B262
Los Alamos National Laboratory
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Fax: (505) 665 4063
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