[Pw_forum] graphite cell optimization failed

[Gabriele Sclauzero]

Dear Giuseppe,

   I think your reply reached also the PW-forum, since I've received it twice, so everyone should have been able to read it.

Il giorno 23/mar/2011, alle ore 10.48, giuseppe.mattioli at mlib.ism.cnr.it ha scritto:

> Dear Gabriele
> 
>>   is there any concrete evidence that "ab initio" van der Waals   
>> vdW-DF is systematically better than Grimme's vdW?
> 
> Yes, at least in the case of molecule-surface interactions.

Maybe graphite is another story... with PBE-D2 you should get an interlayer spacing just 3.4% smaller than the experimental value, which is not so bad considering the much larger PBE error.


> There is a  
> recent (2010) Grimme paper (I'm sorry, I cannot be more accurate  
> today...)

Maybe this one: 
THE JOURNAL OF CHEMICAL PHYSICS 132, 154104 (2010)
which is the paper introducing the D3 method (and a comparison with its predecessor D2)

> that reports an overestimate of the above interactions when  
> using DFT-D2, currently implemented in QE. I've performed comparative  
> tests (classical MM, DFT-D2, vdW-DF) on several molecules interacting  
> with the non-polar 10-10 ZnO surface and I've obtained the best  
> results (some of them comparable with experimental data, i.e., the  
> thiophene ring) by using the vdW-DF approach. The DFT-D2 setup,  
> however, is quite good for molecules in my experience, and can be  
> tuned by changing the C6 coefficients by hand  
> (QE/Modules/mm_dispersion.f90), following one of the available force  
> fields (AMBER, CHARMM, ...).
> Maybe DFT-D3 and vdW-DF would converge to  
> similar results...

I can't tell this, but I know that DFT-D3 should include some notable improvements with respect to the D2 version, since it now takes into account some kind of local coordination of the atoms, atom-pair specific coefficients (from ab initio), and should also separate better the long range regime from the short range one. I know there is someone who offered to look at implementing the extension to D3, maybe it will be available in a few months time.

> What about cp?

No clear idea here. However I believe it should not be difficult to port DFT-D2 to CP, since it requires only atomic positions and the cell setup. These should be handled in a similar way in PW and CP.


Gabriele

> 
> Yours
> 
> G.
> 
> Quoting Gabriele Sclauzero <sclauzer at sissa.it>:
> 
>> Dear Giuseppe,
>> 
>>   is there any concrete evidence that "ab initio" van der Waals   
>> vdW-DF is systematically better than Grimme's vdW?
>> Are you aware of any paper comparing the latest version of the two   
>> methodologies (or "phisolophies", if you want), i.e. vdW-DF2 vs   
>> DFT-D3?
>> 
>> Cheers,
>> 
>> GS
>> 
>> 
>> Il giorno 23/mar/2011, alle ore 10.12,   
>> giuseppe.mattioli at mlib.ism.cnr.it ha scritto:
>> 
>>> 
>>> Dear all
>>> You can do better than the semiempirical "Grimme" correction. There is
>>> a new ab initio van der Waals correlation functional implemented in QE
>>> 4.3a. Try    input_dft='vdW-DF', in the &sysytem list.
>>> By the way, what about a (semiempirical or ab initio) vdW scheme in
>>> cp.x? Is there any project going on?
>>> 
>>> Yours
>>> 
>>> Giuseppe
>>> 
>>> Quoting Masoud Nahali <masoudnahali at gmail.com>:
>>> 
>>>> Dear Eric
>>>> 
>>>> Try london="true" to get improved answer; as you should know DFT is weak
>>>> to calculate dispersion forces and by using the keyword one can include
>>>> these forces semi-empirically. I hope it helps.
>>>> 
>>>> Best Wishes
>>>> 
>>>> Masoud
>>>> --------------
>>>> Masoud Nahali, Sharif University of Technology
>>>> 
>>>> 
>>>> Eric Wrote:
>>>> 
>>>> Dear all,
>>>> 
>>>> I'm trying to optimize unit cell parameter of graphite.
>>>> The problem is the c axis gets too long.
>>>> Starting from published data my initial parameters are a=4.59203 Bohr
>>>> and c=12.513 Bohr.
>>>> The final values are 4.664 and 15.829 respectively.
>>>> I need someone to explain to me what I did wrong, I've attached my input
>>>> file.
>>>> That's a basic calculation so it's very frustrating to not make it done.
>>>> I thank you in advance,
>>>> 
>>>>                                    Eric.
>>>> 
>>>> --
>>>> /Be the change you wish to see in the world
>>>> / --- Mahatma Gandhi ---
>>>> 
>>>> Dr. Éric Germaneau <mailto:germaneau at gucas.ac.cn
>>>> <http://www.democritos.it/mailman/listinfo/pw_forum>>
>>>> 
>>>> College of Physical Sciences
>>>> Graduate University of Chinese Academy of Sciences
>>>> Yuquan Road 19A
>>>> Beijing 100049
>>>> China
>>>> 
>>> 
>>> Giuseppe Mattioli
>>> ISM-CNR
>>> Italy
>>> 
>>> 
>>> 
>>> 
>>> _______________________________________________
>>> Pw_forum mailing list
>>> Pw_forum at pwscf.org
>>> http://www.democritos.it/mailman/listinfo/pw_forum
>> 
>> 
>> § 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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