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Dear Peng Tao,
<div><br>
</div>
<div>as M<span class="Apple-style-span" style="font-size: 12px; ">ohnish Pandey has reported,</span> cell_dofree = 'xy' is not the right option for you.</div>
<div><span class="Apple-style-span" style="font-size: 12px; "><br>
</span></div>
<div><span class="Apple-style-span" style="font-size: 12px; ">In recent versions of QE (I don't know if already in 5.0.2, for sure in the SVN version) there is the </span></div>
<div><span class="Apple-style-span" style="font-size: 12px; ">cell_dofree = '2Dxy' </span></div>
<div><span class="Apple-style-span" style="font-size: 12px; ">option that allows the first two cell vectors to freely change on the plane (i.e. both the x and y coordinates of the first two vectors are free to move), that is what you want.</span></div>
<div><span class="Apple-style-span" style="font-size: 12px; "><br>
</span></div>
<div><span class="Apple-style-span" style="font-size: 12px; ">If you have an old version that does not accept this option, you may want to switch to a recent version of QE, or simply add the following lines to you Modules/cell_base.f90 file (and recompile)</span></div>
<div><span class="Apple-style-span" style="font-size: 12px; "><br>
</span></div>
<div><span class="Apple-style-span" style="font-size: 12px; ">
<div> CASE ('2Dxy')</div>
<div> iforceh = 0</div>
<div> iforceh(1,1) = 1</div>
<div> iforceh(2,2) = 1</div>
<div> iforceh(1,2) = 1</div>
<div> iforceh(2,1) = 1</div>
<div><br>
</div>
<div>(see here to discover where to put these lines: </div>
<div><a href="http://qe-forge.org/gf/project/q-e/scmsvn/?action=browse&path=%2Ftrunk%2Fespresso%2FModules%2Fcell_base.f90&view=markup">http://qe-forge.org/gf/project/q-e/scmsvn/?action=browse&path=%2Ftrunk%2Fespresso%2FModules%2Fcell_base.f90&view=markup</a></div>
<div>)</div>
<div><br>
</div>
<div>Best,</div>
<div>Giovanni Pizzi</div>
<div><br>
</div>
</span></div>
<div><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; ">
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<div>-- </div>
<div>Giovanni Pizzi<br>
Post-doctoral Research Scientist<br>
EPFL STI IMX THEOS<br>
MXC 340 (Bātiment MXC)<br>
Station 12<br>
CH-1015 Lausanne (Switzerland)<br>
Phone: +41 21 69 31124<br>
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<br>
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</span><br class="Apple-interchange-newline">
</span><br class="Apple-interchange-newline">
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<br>
<div>
<div>On 3 May 2013, at 02:26, mohnish pandey wrote:</div>
<br class="Apple-interchange-newline">
<blockquote type="cite">
<div dir="ltr">
<div>Dear Peng,<br>
<br>
</div>
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'.</div>
<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">On Fri, May 3, 2013 at 4:13 AM, Peng Tao <span dir="ltr">
<<a href="mailto:ptao10b@imr.ac.cn" target="_blank">ptao10b@imr.ac.cn</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Dear all,<br>
<br>
Recently, I just want to putting 'vc-relax' to optimize the graphene structure,<br>
but it repots an error:<br>
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%<br>
from checkallsym : error # 2<br>
not orthogonal operation<br>
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%<br>
<br>
And I set 'cell_dofree = xy' in the vc-relax run.<br>
<br>
I know, it is no need to apply vc-relax to graphene, and only relax can aquire<br>
my result. But if I want to relax bi-layer and mutilayer graphene and my ultimate<br>
goal is to get their phonon dispersion curves(so the symmetry should not be broken),<br>
how could I do? Is there any convienient method to relax them?<br>
<br>
Thanks a lot.<br>
<br>
Yours,<br>
Peng Tao<br>
<br>
--<br>
-------------------------------------------------------------------<br>
PH.D. candidate Peng Tao<br>
Magnetism and Magnetic Materials Division<br>
National Laboratory for Material Science<br>
Institute of Metal Research, Chinese Academy of Sciences<br>
Phone <a href="tel:%2B86-024-83978751" value="+862483978751">+86-024-83978751</a><br>
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<br>
-- <br>
Regards,<br>
MOHNISH,<br>
-----------------------------------------------------------------<br>
Mohnish Pandey,<br>
PhD Student,<br>
Center for Atomic Scale Materials Design,<br>
Department of Physics,<br>
Technical University of Denmark<br>
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