[Pw_forum] The question about difference between diamond and graphite

[Gabriele Sclauzero]

How different are your optimized structural parameters from those reported in the literature? 
Looking at your input file, I would suggest to test convergence with degauss, maybe 0.05 (Rydberg!) is too large. Also try shifted k-points meshes, they should give faster convergence.

HTH

GS


Il giorno 06/mag/2011, alle ore 11.20, Alexander G. Kvashnin ha scritto:

> Dear PWSCF community
> 
> In my study I got a problem which I can't solve by myself,
> unfortunately. I hope you can give me some tips where I made a
> mistake. I have to to investigate the energy difference between
> graphite and diamond, but I can't get trusted result.First of all, I
> used LDA PP (PZ), I tested it by subsequently increasing of energy
> cutoff (from 30 Ry to 120 Ry) as well as increasing of k-points mesh
> (4x4x1 for graphite, 4x4x4 for diamond; 6x6x2 for graphite, 6x6x6 for diamond;
> 8x8x3 for graphite, 8x8x8 for diamond; 10x10x4 for graphite, 10x10x10 for diamond).
> I got the difference between energies of diamond and graphite and tried to understand it
> trend (please, see attached figure). As you can see from the figure
> difference between energy diamond and graphite is almost zero so I
> can't say with confidence what structure is more favorable.
> This result different from other theoretical and experimental
> studies, therefore it seems that I did something wrong...
> 
>  My result: ~ 0.001±0.001 eV/atom
> 
>  _______________________________________________
> 
> | Energy difference (eV/atom) | Method      |  Reference     |
> |            0.03                        |Experiment | PRB29_6996  |
> |            0.01                        |  LDA-PP    | PRB29_6996  |
> |            0.04                        |  LDA-PP    | PRB54_14994|
>  -----------------------------------------------------------------------------------
> 
> Input files for diamond and graphite are attached to the letter.
> 
> 
> -- 
> Sincerely yours
> Alexander G. Kvashnin
> --------------------------------------------------------------------------------------------------------------------------------
> First year of master degree study
> Moscow Institute of Physics and Technology          http://mipt.ru/
> 141700, Institutsky lane 9, Dolgoprudny, Moscow Region, Russia
> 
> Junior research scientist
> Technological Institute for Superhard
> and Novel Carbon Materials                                   http://www.ntcstm.troitsk.ru/
> 142190, Central'naya St. 7a, Troitsk, Moscow Region, Russia
> ================================================================
> 
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§ Gabriele Sclauzero, EPFL SB ITP CSEA
   PH H2 462, Station 3, CH-1015 Lausanne

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