[Pw_forum] Grimme C_ij for epitaxial graphene
matthieu.fortin-deschenes at polymtl.ca
Fri May 13 19:11:36 CEST 2016
Paolo and Martin,
Thanks a lot for the advice, I am now looking at the details of how to do it.
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.
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
>> 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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>> Pw_forum at pwscf.org
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