[Pw_forum] symmetries during a vc-relax

JAY Antoine Antoine.JAY at isae-supaero.fr
Mon Oct 2 16:25:37 CEST 2017

Dear devellopers, dear all,
I would like to perform a vc-relax that concerves the point group of each atom and the symmetry of the cell.
I know it is possible to impose symmetries on the BZ's k-points or to fix some atoms coordinates, but this does not give the expected result.
For example,  in a trigonal cell, ibrav 5 imposes the symmetries:
v1 = a(tx,-ty,tz)
v2 = a(0,2ty,tz)
v3 = a(-tx,-ty,tz)
but these symmetries seem to be broken by the relaxation,
so that at the end of the relaxation, v2(1) is not exactelly null and v1(1) is not exactelly -v3(1),
or for the atomic positions, a coordinate (x, x, x) alat becomes (x, 0.99 x, 1.001x ).

?? Is it possible to impose that these constraints on the unit-cell and on the atomic positions stay fix during the relaxation process ??

This is a major issue for the use of these relaxed values in a second step for phonons for example, because it will then not detect the symmetries.
I think it could be a good idea to add into the vc-relax output file a lign that gives the corresponding celldm(i) and not only the CELL_PARAMETERS.
In fact, in the scf before the phonon use, we would like to have ibrav =/0 and celldm in state of ibrav 0 and quasi symmetric CELL_PARAMETERS...

Best regards,

Antoine Jay


Save the date le 14 octobre 2017 : Venez dÿÿcouvrir l'ISAE-SUPAERO de 10h ÿÿ 18h pour les portes ouvertes du leader mondial de la formation en ingÿÿnierie aÿÿrospatiale.
Rencontre avec Thomas Pesquet, diplÿÿmÿÿ Supaÿÿro 2001, au programme. Plus d'infos sur isae-supaero.fr

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20171002/11805206/attachment.html>

More information about the users mailing list