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 > ------------------------------------------------------------------- > > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > -- Regards, MOHNISH, ----------------------------------------------------------------- Mohnish Pandey, PhD Student, Center for Atomic Scale Materials Design, Department of Physics, Technical University of Denmark ----------------------------------------------------------------- -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20130503/02743303/attachment.html
