[QE-users] Error related to point group symmetry

[Pietro Delugas]

Dear Anindya

for static pwscf computations the result should be the same no matter if 
some symmetry is actually used in the program or not. The set  of 
k-points used for the Brillouin-zone sum will be larger when symmetries 
are discarded right in order to preserve all the  actual symmetries  of 
the system.

When the symmetries are not enforced explicitely, there can be some 
small numerical error which step by step can spoil the structural 
relaxation. So  i would  perform the relaxation using the use_all_frac 
options and then use the obtained structure to perform  an scf 
computation setting use_all_frac = .false.  The total energy obtained in 
this latter calculation should be the same as the one obtained in final 
computation performed at the end of the relaxation.

You can then use the scf calculation with use_all_frac = .false. to 
startup the phonon calculations.



On 30/07/2018 11:15, Anindya Bose wrote:
> Dear Dr Stefano Baroni,
> I have tried this method by using the card use_all_frac=.true., in 
> relax,scf and I got the correct point group symmetry however this 
> causing trouble in the phonon and epw calculations.Is there any trade 
> off which I can make to have the calculation symmetrically and 
> technically correct for the higher level computation(like phonon,epw 
> etc).Can't I have a Graphene script from VNL ATK Quantumwise with all 
> the possible corrections.I will be waiting for your response.
>
> Thanks and regards,
> Anindya Bose
> Research Fellow,
> Indian Institute of Information Technology Allahabad.
>
> On Fri, Jul 27, 2018 at 8:52 PM, Stefano Baroni <baroni at sissa.it 
> <mailto:baroni at sissa.it>> wrote:
>
>     Please, have a look at this note and see if you find a fix.
>     http://www.quantum-espresso.org/Doc/pw_user_guide/node21.html#SECTION000600190000000000000
>     <http://www.quantum-espresso.org/Doc/pw_user_guide/node21.html#SECTION000600190000000000000>
>     If you do, please let us know. Regards — SB
>
>>     On 27 Jul 2018, at 12:26, Anindya Bose <anindya at iiita.ac.in
>>     <mailto:anindya at iiita.ac.in>> wrote:
>>
>>     Dear Experts,
>>     Please suggest me a way to resolve this issue.
>>
>>     Thanks and regards,
>>     Anindya Bose
>>
>>     On Monday, July 23, 2018, Anindya Bose <anindya at iiita.ac.in
>>     <mailto:anindya at iiita.ac.in>> wrote:
>>     > Dear Experts,
>>     > I am facing a problem with point group symmetry error.Actually
>>     While doing the vc-relax and scf calculation of Graphene, my
>>     relax.out and scf.out file gives wrong point group information
>>     D_2h(mmm) rather than d3h(the correct one) and even my scf.out
>>     and ph.out showing a wrong point group information C_s(m).
>>     >
>>     > The results are enclosed in the following(relax.out)
>>     >     point group C_s (m)
>>     >      there are  2 classes
>>     >      the character table:
>>     >
>>     >        E     s
>>     > A'     1.00  1.00
>>     > A''    1.00 -1.00
>>     >
>>     >      the symmetry operations in each class and the name of the
>>     first element:
>>     >
>>     >      E        1
>>     >           identity
>>     >      s        2
>>     >           inv. 180 deg rotation - cart. axis [0,0,1]
>>     >
>>     >
>>     > I have tried a lot to change my structure but I am still unable
>>     to resolve this issues.If anyone faced the same issue related to
>>     point group symmetry error then please help me to solve this
>>     difficulty.I will be waiting for the response.
>>     > Thanks and regards,
>>     > Anindya Bose
>>     > Research Fellow,
>>     > Indian Institute of Information Technology Allahabad.
>>     >
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>
>     —
>     Stefano Baroni - Trieste — http://stefano.baroni.me
>     <http://stefano.baroni.me>
>
>
>
>
>
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