[CP2K:5421] Binding energy of graphene bilayer: CHARMM vs. DFT-D3

[Robert Yang]

Dear Juerg,

thank you for your response.

On Friday, June 20, 2014 4:47:27 PM UTC+2, jgh wrote:
>
> Hi 
>
> - first question: What is the value given in literature? 
>   I'm sure there are others that have calculated this. 
>

The values given by other DFT calculation are around 40 meV/atom. But it is 
not clear whether they normalized the total binding energy by the total 
number of atoms in both layers or in a single layer. If normalized by the 
atom number in bi-layer, my DFT result is close to reported results. If 
normalized by atom number in a single layer, my classical result sounds to 
be correct.
 

>
> - Are your values based on a single geometry (and stacking) or 
>   did you optimize geometry and cell size? 
>
 
Actually I had done more calculations, for instance the dependence of the 
binding energy on the vertical distance between the two layers, and the 
variation of the binding energy with the lateral sliding between layers.
 

> - Your relative cutoff is rather low (25). 
>

For such a pure carbon system, would this value of relative cutoff be 
enough?  I am going to do other simulations with higher cutoff, would 100 
be OK? 

But I am wondering the cutoff value will give such a big influence, the 
current DFT result is two times of that of classical FF calculation. 

Thanks again for the response!

Best wishes,
Robert


> Without further information we don't know where to look for 
> a problem. 
>
> regards 
>
> Juerg 
> -------------------------------------------------------------- 
> Juerg Hutter                         Phone : ++41 44 635 4491 
> Institut für Chemie C                FAX   : ++41 44 635 6838 
> Universität Zürich                   E-mail: hut... at chem.uzh.ch 
> Winterthurerstrasse 190 
> CH-8057 Zürich, Switzerland 
> --------------------------------------------------------------- 
>
> -----cp... at googlegroups.com wrote: ----- 
> To: cp... at googlegroups.com 
> From: Robert Yang 
> Sent by: cp... at googlegroups.com 
> Date: 06/18/2014 09:24PM 
> Subject: [CP2K:5421] Binding energy of graphene bilayer: CHARMM vs. DFT-D3 
>
> Dear all, 
>
> I am calculating the binding energy of graphene bilayer of the size 
> 3nmX3nm (2X416 atoms). It turns out that the result from calculations with 
> classical force field is quite different from that of DFTs: 
>
> CHARMM FF:                                       -0.579 Hartree 
> DFT-D3:                                                -1.056 Hartree 
> DFT-D3 with BSSE correction:           -0.968 Hartree 
>
> It is quite strange that the value of CHARMM is nearly one half of DFT 
> results. 
>
> The binding energy is defined here as: dE = E_bilayer - 2*E_single_layer. 
>
> All my input files are attached in the tar file. Please help me to find 
> out where the problem lies in. Thank you! 
>
> Best wishes, 
> Robert 
>   
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> [attachment "t.tar" removed by Jürg Hutter/at/UZH] 
>
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