[Pw_forum] change of crystal symmetry during vc-relax calculations with pressure

Paolo Giannozzi paolo.giannozzi at uniud.it
Fri Jun 14 12:34:57 CEST 2013

On Fri, 2013-06-14 at 09:13 +0000, saqib javed wrote:

> i started with tetragonal structure (ibrav=6) so i would have imagined
> that a=b would have been enforced by the code in case symmetry is
> conserved during optimization ...

symmetry IS conserved during optimization, apart from unfortunate cases,
but only the symmetry of the starting configuration, as found by the
code. Look at which symmetries are found by the code in the starting

> you are saying that these results don't represent physical
> pressure-induced tetragonal to orthorhombic transition but just a
> numerical artificat ?

I don't know. Likely: it is a 0.3% difference. Do you trust it?
I wouldn't. At least, not without some additional evidence.

 Paolo Giannozzi, Dept. Chemistry&Physics&Environment, 
 Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
 Phone +39-0432-558216, fax +39-0432-558222 

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