[Pw_forum] Relax Linear chain with constraint

[Marco Di Gennaro]

Dear Federico,

your suggestion is indeed correct.
I am now using this to solve my problem:
ATOMIC_POSITIONS (ang)
Si 0.25 0.25 0.25  1 0 0
Si 0.0 0.0 0.0        1 0 0

best regards

Marco Di Gennaro, Dr.
Nccr MARVEL - University of Basel
Phone +41 61 267 3846
Klingelbergstrasse 80, Office 5.10


________________________________________
From: pw_forum-bounces at pwscf.org [pw_forum-bounces at pwscf.org] on behalf of Federico Iori [federico.iori at u-psud.fr]
Sent: Wednesday, May 24, 2017 6:02 PM
To: PWSCF Forum
Subject: Re: [Pw_forum] Relax Linear chain with constraint

Hi Marco.

If I correctly understood, if you want to relax *only* some of yours atoms, you should impose some constrains in the ATOMIC_POSITIONS


http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html#idm140629872010784

see

if_pos(1), if_pos(2), if_pos(3)     INTEGER
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 MD dynamics or
    structural optimization run.

    With crystal_sg atomic coordinates the constraints are copied in all equivalent
    atoms.


Example:

ATOMIC_POSITIONS (ang)
Si 0.25 0.25 0.25 0 0 0  --> this will not move
Si 0.0 0.0 0.0        1 1 1  --> this will move

[Université Paris-Sud]
Federico IORI
Marie Curie Fellow
Laboratoire de Physique des Solides
Bâtiment 510 - Rue André Rivière
91400 Orsay



________________________________
De: "Marco Di Gennaro" <marco.digennaro at unibas.ch>
Para: "pw forum" <pw_forum at pwscf.org>
Enviados: Miércoles, 24 de Mayo 2017 17:45:45
Asunto: [Pw_forum] Relax Linear chain with constraint

Dear PW users,

I would like to relax my system while keeping some geometry constraints.

Specifically, I have a linear chain composed of N atoms (say A,B,C).
I want to know if it is possible to relax the distance among atoms only (so AB, BC and CA)
while making sure that the system stays linear after the relaxation.

Following the PW doc: http://www.quantum-espresso.org/wp-content/uploads/Doc/pw_user_guide/node11.html
I have tried with calculation='relax' and add namelist &IONS,
but it looks like there is no relaxation at all.

Thank you,
Marco Di Gennaro, Dr.
Nccr MARVEL - University of Basel
Phone +41 61 267 3846
Klingelbergstrasse 80, Office 5.10


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