[Pw_forum] lattice parameter in 'vc-relax' mode doesn't change

[Vincenzo Verdolino]

As Paolo was mentioning I would suggest you to

grep -A 3 'CELL_PARAMETERS' output.out

you should get something like

CELL_PARAMETERS (alat= 22.67671359)
   0.971595358  -0.004204137   0.034718207
  -0.003973715   0.993274472  -0.003814071
   0.073550426  -0.008394064   2.103660061
--
CELL_PARAMETERS (alat= 22.67671359)
   0.971710425  -0.004267871   0.034659977
  -0.004044929   0.992889770  -0.003977620
   0.073404775  -0.008729724   2.103161050
--
CELL_PARAMETERS (alat= 22.67671359)
   0.971566286  -0.004317083   0.035948125
  -0.004085492   0.992305284  -0.003891887
   0.076105646  -0.008563323   2.103332063
--

as you see alat is constant because it's the starting value but parameters
(ptimitive vector) change

you should be able to get back the cell parameter in the form A= , B= , C=
, cosAB= , cosAC =, cosBC=

vincenzo


On Tue, Aug 19, 2014 at 11:28 AM, Paolo Giannozzi <paolo.giannozzi at uniud.it>
wrote:

> On Sun, 2014-08-17 at 02:33 +0000, Sokseiha Muy wrote:
>
> > I'm using QE to study the properties of BaF2 which is a cubic
> > material. I notice that when I used the option 'vc-relax' to optimized
> > my structure, in the output the volume of the unit cell change as
> > expected but the lattice parameter is the same for every step.
>
> the lattice parameter is set to its starting value. It is the length
> of the primitive vectors that changes. Look for the primitive vectors
> in the output: they are reprinted in various places and formats.
>
> P.
> --
> 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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