[Pw_forum] Relax Linear chain with constraint

[Federico Iori]

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 

	
Federico IORI 
Marie Curie Fellow 
Laboratoire de Physique des Solides 
Bâtiment 510 - Rue André Rivière 
91400 Orsay 


----- Mensaje original -----

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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