[Pw_forum] Variable cell
Stefano de Gironcoli
degironc at sissa.it
Wed Dec 17 13:20:04 CET 2008
how many symmetry operations are found by the code ?
stefano
Eyvaz Isaev wrote:
> Dear developers and users,
>
> I am quite agree there is no time to submit any question, it is time to be prepared to incoming X-Mas.
>
> Nevertheless, sorry, one question. I am doing variable-cell calculations by means of damp-w option.
> Initial choice for the lattice is ibrav=12, i.e. simple monoclinic. As far as I know the (Wentzcovitch) method should not change the cell shape (i.e. basis vectors will not change their symmetry). As it is mentioned in the original paper "... eliminate symmetry breaking"
>
> But it seems to be not the case for a mononclinic cell, as initial basis vectors are:
>
> a1 = 1 0 0
> a2 = 0.0340004 0.999671 0
> a3 = 0 0 0.999225
>
> then right after the first step (i.e. damp-w starts) these vectors become
>
> a1 = 0.999348118 -0.000624697 0.
> a2 = 0.029359585 0.999030676 0
> a3 = 0 0 0.998400159
>
> I expected basis vectors will keep the original symmetry, though a1 seems to be changed. For tetragonal symmetry there is no such kind problem.
>
> I have just tested it using v.4.0.4, the same result.
>
> It would be very nice if someone can explain me why this happens for a monoclinic cell. May be there is some misunderstanding of mine side.
>
> Bests,
> Eyvaz.
>
> -------------------------------------------------------------------
> Prof. Eyvaz Isaev,
> Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia,
> Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden
> Condensed Matter Theory Group, Uppsala University, Sweden
> Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com
>
>
>
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