[Pw_forum] The question about difference between diamond and graphite

[Gabriele Sclauzero]

Il giorno 11/mag/2011, alle ore 11.58, Gabriele Sclauzero ha scritto:

> 
> 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.

Moreover smearing is not needed for diamond, since it has a large band gap, while graphene could also be converged without smearing or with a very small spread.

> 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
>> ================================================================
>> 
>> <input_diamond.opt><input_graphite.opt><Energy_difference.GIF>_______________________________________________
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> 
> 
> § Gabriele Sclauzero, EPFL SB ITP CSEA
>    PH H2 462, Station 3, CH-1015 Lausanne
> 
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§ Gabriele Sclauzero, EPFL SB ITP CSEA
   PH H2 462, Station 3, CH-1015 Lausanne

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