[Pw_forum] 回覆： Re: [Pw_forum] How to calculate the relaxation calculation by setting one of the atomic coordinate fixed???

[Lawrence Lee]

Hi Eyvaz.,

I've tried this method (doing relaxation while holding some atoms fixed) long ago when I started learning using PWSCF. But the problem was that the number of iterations needed in this case is much much more than if I set all atoms free!! I have this problem in my mind since then. Do any one know why?

Thank you!

Lawrence

Eyvaz Isaev <eyvaz_isaev at yahoo.com> 說： Hi Prithwish,

You can do it easily. From INPUT_PW:
    X  x y z   {if_pos(1) if_pos(2) if_pos(3)}
  where :
    X         Character: label of the atom as specified in ATOMIC_SPECIES
    x, y, z   Real: atomic positions
    if_pos:   Integer, optional ( default = 1 ): component i of the force for
              this atom is multiplied by if_pos(i), which must be either 0 or 1.
              Used to keep selected atoms and/or selected components  fixed in
              meta-dynamics, neb, smd, MD dynamics or structural optimization
              run.
I.e. like this where Al atom is supposed to be relaxed, but As atom not.

Al 0.5 0.5 0.5 1 1 1
...........................
As  0 0 .5   0 0 0

Bests,
Eyvaz.
P.S. By the way there is no need to duplicate your message.

----- Original Message ----
From: Prithwish Nandi <pnspeaks at sify.com>
To: pw_forum at pwscf.org
Sent: Thursday, April 5, 2007 1:38:55 PM
Subject: [Pw_forum] How to calculate the relaxation calculation by setting one of the atomic coordinate fixed???


  Hi, 
     I want to do a relaxation calculation of a 32
  atom
cell by keeping one atom at a fixed position and other 31 atoms to be
relaxed.Is it possible to do the problem by setting X-iforce,Y-iforce
and Z-iforce equals to 1 for 31 atoms and by not setting for the atom I
want to be fixed ? Or, there is some other procedures for doing the job?
Please help.


  Prithwish Nandi
  Research Scholar
  IGCAR,
Kalpakkam, India
   
  

  
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