[Pw_forum] VC-Relax taking too long on a 4-atom system

[Juanjo Meléndez]

Hi Elliot

Assuming that you calibrated correctly both cutoff, ecutrho and the ZB 
sampling, I have a few suggestions which could help you:

1) Are you sure about the value at "celldm(1)" and about your atomic 
positions? Take into account that your are using the {alat} switch, which 
means that you are providing cartesian coordinates in units of the lattice 
parameter. You should also check the CELL_PARAMETERS card.

2) Change "nat=1" by "nat=4", because these are the atoms that your unit 
cell actually contains.

3) Do not use "nosym=.true.", because your system has some symmetries that 
may simplify the calculations.

4) Do not use "dipfield" for your calculations. See the input data 
description for an explanation.

Hope these suggestions help you. Additionally, I would not use so many 
cycles (10^6 is a lot!). Convergence should be achieved in less than (or 
about) 100 cycles. If you force a high number of cycles, you will not 
realize whether there is something wrong in your starting model...

Good luck

Juanjo


Juan J. Meléndez
Associate Professor
Department of Physics · University of Extremadura
Avda. de Elvas, s/n 06006 Badajoz (Spain)
Phone: +34 924 28 96 55
Fax: +34 924 28 96 51
Email: melendez at unex.es
Web: http://materiales.unex.es/miembros/personal/jj-melendez/Index.html



-----Mensaje original----- 
From: Elliot Menkah
Sent: Wednesday, October 22, 2014 4:04 PM
To: pw_forum at pwscf.org
Subject: [Pw_forum] VC-Relax taking too long on a 4-atom system

Hi Everyone,
I'm trying to determine a lattice parameter in a study and I'm running a
vc-relax calculation.
It's just a 4-atom bulk ferromagnetic nickel system yet my calculation
has been running for over 5hrs already on a 16 core resource.

It's presently on ' iteration #*** '

Is there anything wrong with the setup of the job?

Shouldn’t the job have completed by now?

Could you please peruse and vet my input file for any possibles reasons
why it's so if it shouldn’t be?

What could be affecting the convergence?


Thank you




Kind Regards,

Elliot

-- 
Elliot S. Menkah
Research Student - Computational Chemistry/ Computational Material Science
Theoretical and Computational Chemistry
Dept. of Chemistry
Kwame Nkrumah UNiversity of Sci. and Tech.
Kumasi
Ghana

Tel: +233 243-055-717

Alt Email: elliotsmenkah at gmail.com
           elliotsmenkah at hotmail.com








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