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

[Jian-Xin Zhu]

Dear Jonathan and Nicola, 

I looked into my *.win file. It looks the k-values in this file do not pose the precision issue (eg 0.666 vs 0.66666666666). 

....
 begin kpoints
  0.000000000  0.000000000  0.000000000
  0.000000000  0.000000000  0.125000000
  0.000000000  0.000000000  0.250000000
  0.000000000  0.000000000  0.375000000
  0.000000000  0.000000000  0.500000000
  0.000000000  0.000000000  0.625000000
  0.000000000  0.000000000  0.750000000
  0.000000000  0.000000000  0.875000000
  0.000000000  0.125000000  0.000000000
  0.000000000  0.125000000  0.125000000
  0.000000000  0.125000000  0.250000000
  0.000000000  0.125000000  0.375000000
  0.000000000  0.125000000  0.500000000
  0.000000000  0.125000000  0.625000000
  0.000000000  0.125000000  0.750000000
  0.000000000  0.125000000  0.875000000
  0.000000000  0.250000000  0.000000000
  0.000000000  0.250000000  0.125000000
  0.000000000  0.250000000  0.250000000
  0.000000000  0.250000000  0.375000000
  0.000000000  0.250000000  0.500000000
  0.000000000  0.250000000  0.625000000
  0.000000000  0.250000000  0.750000000
  0.000000000  0.250000000  0.875000000
....

I understand you want me to run kmesh.pl and paste the generated k-values into the corresponding block of *.win file. 
I have tested the script file. It seems the generated k-values do not improve the precision much as compared with the above listed. 

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). 
Instead, the way as suggested by Philip by increasing the value of kmesh_tol (e.g., from 0.000001 to 0.001) might be a simple fix. 


Best regards, 

Jianxin













On Nov 16, 2010, at 5:03 PM, Jonathan Yates wrote:

> 
> On 16 Nov 2010, at 20:02, Jian-Xin Zhu wrote:
> 
>> Dear Wannier users, 
>> 
>> Sometimes when I run wannier90.x -pp case, 
>> 
>> I get the following error as written to case.wout file 
>> 
>> ....
>> Exiting.......
>> Eq. (B1) not satisfied in kmesh_get (1)
>> .....
>> 
>> What's the reason for this type of error and how can I get it resolved?
> 
> Jianxin,
> 
> The code is trying to find a good set of b-vectors to make a finite difference representation of the position operator (see the CPC article for technical details). It has done this successfully for the gamma point, but has failed when trying to use those b-vectors for the other k-points in the grid. This could be caused by not specifying the k-points to sufficient precision in the win file (eg 0.666 vs 0.66666666666). There is a script in the utilities directory called kmesh.pl that will write the k-points with sufficient precision.
> If this does not resolve the problem, please post the win file.
> 
> Yours
>  Jonathan
> 
> 
> 
> 
> -- 
> Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK
> tel: +44 (0)1865 612797                http://users.ox.ac.uk/~oums0549/
> 
> _______________________________________________
> Wannier mailing list
> Wannier at quantum-espresso.org
> http://www.democritos.it/mailman/listinfo/wannier

-- 
###############################
Jian-Xin Zhu, Ph.D
Theoretical Division, MS B262
Los Alamos National Laboratory
Los Alamos, New Mexico 87545
Phone: (505) 667 2363
Fax: (505) 665 4063
Email (main): jxzhu at lanl.gov
Email (backup): physjxzhu at gmail.com
URL: http://theory.lanl.gov
###############################