[Pw_forum] Questions about ionic & cell relaxation.

Nicola Marzari marzari at MIT.EDU
Thu Jan 17 22:36:13 CET 2008

Hongbin Zhang wrote:
> Dear all pwscf users,
> I want to do some ionic relaxations, but there's one question unclear:
> Will the relaxation lower the original symmetry?

Ionic forces will satisfy all the symmetry operations that PWSCF
has found, and so relaxations will preserve those symmetry operations.

Generally speaking, you should be fine - if anything, one needs
to be careful of the opposite problem, when the ionic ground state has
less symmetry than the initial configuration (since the relaxations
do not break the symmetry).


> The reason why I ask this is that I want to optimize the cell and ionic
> positions with some constraints, say, to keep the mirror symmetry along
> z direction of the unit cell.
> Any suggestion and comment are welcome. Thank you in advance.
> Best wishes,
> Hongbin Zhang
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Prof Nicola Marzari   Department of Materials Science and Engineering
13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu

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