[Pw_forum] Graphene Structural Relaxation

[Gabriele Sclauzero]

On 08/18/2010 12:54 AM, meysam pazoki wrote:
>
>
> ---------- Forwarded message ----------
> From: *meysam pazoki* <meysam.pazoki at gmail.com 
> <mailto:meysam.pazoki at gmail.com>>
> Date: Tue, Jul 20, 2010 at 11:46 PM
> Subject: Graphene Structural Relaxation
> To: pw_forum-request at pwscf.org <mailto:pw_forum-request at pwscf.org>
>
>
> Dear PWSCF users
> I have a problem in relaxation of grahene super cell with 24 atoms. In 
> relaxation procedure ,graphene hooney-comb structure completely 
> destroys and atoms have no regular ordering after relaxation 
> procedure.I use pbe-rrkjus psudopotential,4 3 3 kpoint grid,30 rydberg 
> cutff energy,300 rydberg ecutrho.
> I use both ion_damps & bfgs algorithms and get similar results.
> If i change the ecutrho to 100, atoms have an irregular positions in 3 
> dimension,but when ecut rho set to 300 atoms have irregular position 
> in-plane.
> furthermore if i set 
> :trust_radius_ini=.1D0,trust_radius_max=.3D0,bfgs_ndim = 3,
> I have the honeycomb structure but some of c atoms exprience great 
> forces like:
>
> atom 19 type 1 force = 11948.08469282 -219.69802882 0.00000000
>
> atom 20 type 1 force = 11782.00343549 12.01959200 0.00000000
>
> atom 21 type 1 force = 11748.09287051 115.25218004 0.00000000
>
> atom 22 type 1 force = 11241.09464255 -222.56999757 0.00000000
>
> atom 23 type 1 force = -0.50941109 0.26861287 0.00000000
>
> atom 24 type 1 force = 11905.77649683 -91.34763119 0.00000000
>

These forces are simply crazy... I mean, if the units are those used by 
PWscf (Ry/Bohr) the forces that you are reporting are huge! If you have 
used the PP on the QE website, then the atomic positions and/or the cell 
dimensions that you have supplied to PWscf  must be far off the 
equilibrium ones. Please provide an input file.

GS

> My question is what is wrong in my structure relaxation procedure that 
> result in such non-physical data.
>
> It would appreciated if anyone can help me in this problem
> Thanks in advance
> meysam pazoki
> Ph.D student of physics
> Sharif university of technology
>
>
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-- 

Gabriele Sclauzero, EPFL SB ITP CSEA
PH H2 462, Station 3, CH-1015 Lausanne

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