[Pw_forum] How to Fix certain atoms in relax calculation?

[Axel Kohlmeyer]

On 5/22/06, lan haiping <lanhaiping at gmail.com> wrote:
>
> Hi ,
>
>    i wanna do some  relaxation calculations with some atoms fixed, but i
> donot know how to in PWSCF.
> I have tried to read the Doc/INPUT_PW, and was confused that "if_pos(i)"
> with 1 and CONSTRAINT CARDS might realize my goal.   Would you please give
> me some hints about these two differences ?

if you just want to fix positions in space, if_pos(i) is the method to use.
just after the coordinates you can put 3 numbers or x-, y-, and z-component.
in each md or relax step, the corresponding force component for that coordinate
is multiplied with the factor you give. i.e. an atom can freely move
with a  1 1 1
and will be frozen with 0 0 0. using, e.g.,  1 1 0 will only allow
movement in xy-plane
0 0 1 only in z-direction and so on.

CONSTRAINT_CARDS is for e.g. distance constraint and similar stuff.

regards,
     axel.
>  Regards,
>
> Hai-Ping
>
>


-- 
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Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
  Center for Molecular Modeling   --   University of Pennsylvania
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tel: 1-215-898-1582,  fax: 1-215-573-6233,  office-tel: 1-215-898-5425
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