[Pw_forum] fixing the angle.

Lorenzo Paulatto paulatto at sissa.it
Mon Nov 2 10:25:18 CET 2009

On Mon, November 2, 2009 10:13, Bipul Rakshit wrote:
>  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.

I don't have any.

>  Actually after running vc-relax with the input file which i send to you,
>  the CELL_PARAMETER changes, that means angle also changing....

Of course, if you squeeze the cell along one direction the structure will
deform accordingly. If you want to rescale the whole structure maintaining
all the angles constant you have to change ONLY celldm(1). There is no
automatic way to do it, the cell_dofree input parameter can constrain cell
deformation but not in this way.

>  I draw the output file with xcrysden and find the angles (Si-O-Si)
>  changes.

Yes, I understand what's going on. But what's wrong with it changing in
the first place?

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

I don't have a secret library of input files...

best regards

Lorenzo Paulatto
phone: +39 040 3787 511
skype: paulatz
www:   http://people.sissa.it/~paulatto/

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