[Pw_forum] "not orthogonal operation" during vc-relax when optimizing graphene

[mohnish pandey]

Dear Peng,

The cell you might be using is 'hexagonal' and the 'vc-relax' that you are
doing has two degrees of freedom in x and y direction which are orthogonal
due the flag 'cell_dofree = xy' you set. Since the symmetry is breaking in
the second step due to relaxation in x and y direction it is changing the
number of k-points. That's why you are getting that error. A simple
work-around for this is you use a bit bigger cell with orthorhombic
symmetry (in which you have orthogonal 'a' and 'b' vectors). In
orthorhombic cell symmetry won't break due to 'cell_dofree = xy'.


On Fri, May 3, 2013 at 4:13 AM, Peng Tao <ptao10b at imr.ac.cn> wrote:

> Dear all,
>
> Recently, I just want to putting 'vc-relax' to optimize the graphene
> structure,
> but it repots an error:
>
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>      from checkallsym : error #         2
>      not orthogonal operation
>
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>
> And I set 'cell_dofree = xy' in the vc-relax run.
>
> I know, it is no need to apply vc-relax to graphene, and only relax can
> aquire
> my result. But if I want to relax bi-layer and mutilayer graphene and my
> ultimate
> goal is to get their phonon dispersion curves(so the symmetry should not
> be broken),
> how could I do? Is there any convienient method to relax them?
>
> Thanks a lot.
>
> Yours,
> Peng Tao
>
> --
> -------------------------------------------------------------------
> PH.D. candidate Peng Tao
> Magnetism and Magnetic Materials Division
> National Laboratory for Material Science
> Institute of Metal Research, Chinese Academy of Sciences
> Phone  +86-024-83978751
> -------------------------------------------------------------------
>
>
>
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>



-- 
Regards,
MOHNISH,
-----------------------------------------------------------------
Mohnish Pandey,
PhD Student,
Center for Atomic Scale Materials Design,
Department of Physics,
Technical University of Denmark
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