[Pw_forum] Grimme C_ij for epitaxial graphene

[Matthieu Fortin-Deschênes]

Paolo and Martin,

Thanks a lot for the advice, I am now looking at the details of how to do it.

Martin,

They are metal substrates. I will look at those papers in details. I  
was planning to use both Grimme corrections and a VdW functional to  
compare the results. Thanks again for the advice. Very helpful.

Matthieu

Martin Andersson <ma at nano.ku.dk> a écrit :

> Hi Matthieu,
>
> 		I was curious as to which substrates you are putting graphene on.  
> Because if you are looking at either ionic solids or metals, the  
> Grimme corrections are going to be a bit too strong, but it can be  
> fixed. We have had success for calculating adsorption energies on  
> minerals by reducing the C6 parameter for the cations in the  
> substrate by about an order of magnitude (we decreased the parameter  
> by 33 for Ca in calcite in (Okhrimenko et al Langmuir 29,  
> 11062-11073,(2013)). The idea came from Ehrlich et al ChemPhysChem  
> 12, 3414-3420,(2011). For cations in ionic solids (e.g. oxides,  
> minerals), the polarisability is significantly smaller  because of  
> the smaller electron cloud of a cation compared to the corresponding  
> neutral atom.
>
> 		For metals, I had good success in Andersson MP Journal of  
> Theoretical Chemistry 2013, Article ID 327839,(2013), where I  
> modified Grimme corrections to make it work better for metals by  
> using a shorter cutoff to simulate screening by the conduction  
> electrons and switching the C6 parameters for the metal to the  
> parameter of the noble gas in the row above.
>
> 		In either of the two cases, you only need to modify the  
> mm_dispersion.f90 file and recompile. I have a couple of different  
> mm_dispersion.f90 files lying around if you need one...
>
> 		Or you could of course also switch to a suitable vdw functional if  
> you like instead.
>
> 		Cheers and good luck,
>
> ————————————————————————
> Martin P. Andersson
> Associate Professor
> Nano-Science Center, Department of Chemistry
> University of Copenhagen, Denmark
>
> Tel: +45 3532 0280
> Mobile: +46 733 893091
> E-mail: ma at nano.ku.dk
> ————————————————————————
>
>
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>
>> On 12 May 2016, at 20:22, Matthieu Fortin-Deschênes  
>> <matthieu.fortin-deschenes at polymtl.ca> wrote:
>>
>> Hi all,
>>
>> I'm trying to calculate some basic properties of graphene on various
>> substrates using Grimme correction for VdW interactions. The Grimme
>> corrections seem to deteriorate the results (lattice parameter and
>> binding energy) of the graphene as well of the substrate compared to
>> experimental results.
>>
>> I was wondering if it's possible to set C_ij=0 for i=j (no correction
>> for C-C interactions, as well as substrate-substrate interaction), but
>> non-zero C_ij for graphene-substrate interactions. As far as i know,
>> C_i are defined for each element and C_ij is calculated from
>> sqrt(C_i*C_j). I would like to set all C_ij by myself.
>>
>> Thank you
>>
>> Matthieu Fortin-Deschênes
>> Polytechnique Montreal
>>
>>
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