[Pw_forum] how to optimize the lattice parameters of monoclinic structure ?

[Javad hashemifar]

Dear Fatma
I think the best option for you is the vc (volume-cell) relaxation. In this
kind of calculations all lattice parameters and atomic positions are relaxed
simultaneously. Please see the INPUT_PW file for adjusting the required
input parameters.
another option is to relax lattice parameters one by one. In each step you
should vary one lattice parameter and fix others. After finding the
optimized value of this lattice parameter, it should be fixed and another
lattice parameter should be optimized. The following sequence of relaxation
may be useful:

1. betha (a, b/a, and c/a are fixed to experimental or any other reported
value)
2. Volume (betha, b/a, and c/a should be fixed)
3. b/a (betha, Volume, and c/a are fixed)
4. c/a (bethe, Volume, and b/a are fixed)

it is better to repeat the above sequence more than one time.

It should be noted that vc relaxation seems to be more appropriate for you.

Javad



On Mon, Jul 7, 2008 at 10:52 PM, Fatma Litimein <flitimein at yahoo.fr> wrote:

>   *Dear PWscf users, *  *I have a question about optimization of an
> monoclinic  structure, so to do that have I to optimize c/a, V, b/a, V,
> ...., beta, V,  in SCF manner until convergence of the structure or can I
> perform just one c/a, b/a, V optimization ? How can I to optimize i.e. beta
> angel? Any comments are welcome. *
> *Thank you in advance *
>
>
>
>
> =======================================================
> Fatma Litimein
> Computational Materials Science Laboratory,
> Physics Department, University of Sidi Bel Abbes
> Sidi Bel Abbes, 22000 - Algeria
> Tel:+213 48-54-95-46 Fax:+213 48-54-19-28 flitimein at yahoo.fr
> =======================================================
>
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-- 
======================================
Seyed Javad Hashemifar, Ph.D.
current address:
Physics Department, University of Duisburg-Essen,
47057 Duisburg, Germany
Tel:+49 203 379 4743 Fax:+49 203 379 4741
permanent address:
Physics Department, Isfahan University of Technology
84154 Isfahan, Iran
Tel: +98 311 391 2375 Fax:+98 311 3912376
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