[Pw_forum] fixing the angle.

[Bipul Rakshit]

Dear Lorenzo Paulatto,
Thanks for your kind mail.
I got your points.

I saw the Doc/INPUT_PW.txt file, there is a flag called CARD: CONSTRAINTS in
which there is 'planar_angle' and  'torsional_angle', but it will be more
helpful if you send me one input file for constraining the angle.

Actually after running vc-relax with the input file which i send to you, the
CELL_PARAMETER changes, that means angle also changing....
I draw the output file with xcrysden and find the angles (Si-O-Si) changes.

So if possible just send me some input file for constraining the angles.

On Mon, Nov 2, 2009 at 2:02 PM, Lorenzo Paulatto <paulatto at sissa.it> wrote:

> In data 02 novembre 2009 alle ore 09:15:06, Bipul Rakshit
> <bipulrr at gmail.com> ha scritto:
> > What I want is to optimise the structure, using vc-relax. Beside I also
> > want that, the angle should not change between the atoms and vc-relax
> give me
> > an optimised structure.
>
> Dear Bipul,
> it's not very clear to me which angle do you want to keep fixed, but it
> doesn't really matter.
>
> You can nail the atoms to their initial positions setting the additional
> flags in the atomic position lines; this will work if you are using
> crystal or alat coordinates (you are), it will only allow the cell volume
> to change.
>
> Otherwise you can set a constrain, you can find the documentation in
> Doc/INPUT_PW.txt. It is not difficult at all, but it does not work with
> bfgs, so you'll have to use damp dynamics for the atoms relaxation.
>
> best regards
>
> --
> Lorenzo Paulatto
> SISSA  &  DEMOCRITOS (Trieste)
> phone: +39 040 3787 511
> skype: paulatz
> www:   http://people.sissa.it/~paulatto/<http://people.sissa.it/%7Epaulatto/>
>
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>
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-- 
Dr. Bipul Rakshit
Research Associate,
S N Bose Centre for Basic Sciences,
Salt Lake,
Kolkata 700 098
India
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