[Wannier] Question about searcg_shell: cell too long?

[Han Hsu]

Hello Jonathan,

Thank you for your reponse. Setting larger kmesh_tol works well. In fact,
setting kmesh_tol = 0.000001005 is enough in my case. I guess this is
beacause the structure of my LaCoO3 does not deviate too much from cubic
perovskite...though I am not sure about this.

Before knowing the setting for kmesh_tol, I followed the instruction
written in the *.wout file, that is, setting devel_flag=kmesh_degen and
writing a file for k-point shell. The file includes two shells, which
should be sufficient. However, It did not work wither. 

Regards,

Han
 
> Han,
> 
>   This is subtle problem, and unfortunately the error message is  
> misleading.
> 
> The first two kpoint shells are actually sufficient to satisfy the so- 
> called B1 condition. However, there is not enough precision in the  
> specified lattice vectors, and so we don't quite hit the target  
> accuracy for solving B1. I realise that specifying more sig. fig. in  
> the lattice vectors is tough - but a perfectly reasonable solution is  
> to lower the B1 tolerance: set
>   kmesh_tol=0.00001 (this is 10x > than the default)
>   and it'll work (no need to alter search_shells from the default 12)  
> Note that lowering this tolerance will has no effect on the accuracy  
> of the wannier functions.
> 
> Thanks for pointing this out. In the future we should do two things:
> 
> 1- Make a script to automatically create w90 input from pwscf inputs  
> - and hence always include enough sig. figs.
> 
> 2- The kmesh routine could be smarter; detect when we have only just  
> failed to satisfy B1 and offer a more helpful error message.
> 
>   Yours
>     Jonathan


**********************************************************
Han Hsu, Ph.D.
Postdoctoral Associate
Department of Chemical Engineering & Materials Science
University of Minnesota
http://www.cems.umn.edu/~hsuhan
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