[Pw_forum] Graphene Structural Relaxation

[xirainbow]

Dear meysam pazoki:
Why you choose (4 3 3) kpoint grid.
If you are dealing with monolayer graphene, I think you should change it to
(1 x x).
Furthermore, I do not think (x=3) is enough for graphene.
Maybe you can increase (x) and have a try:)

On Wed, Aug 18, 2010 at 6:54 AM, meysam pazoki
<m_pazoki at physics.sharif.edu>wrote:

>
>
> ---------- Forwarded message ----------
> From: meysam pazoki <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
>
>
> 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
>
> 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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>


-- 
____________________________________
Hui Wang
School of physics, Nankai University, Tianjin, China
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