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Re: [lammps-users] Neighbor list for calculating the local normals for Kolmogorov-Crespi potential
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Re: [lammps-users] Neighbor list for calculating the local normals for Kolmogorov-Crespi potential


From: ouyang <w.g.ouyang@...24...>
Date: Wed, 26 Jul 2017 19:19:58 +0800

Dear Axel,
Thanks! I think it will be OK if there is only KC potential. However, people usually use REBO+KC potential to simulate few layers of graphene. The command is like follows, as is in the documentation of pair_style kolmogorov/crespi/z:
pair_style     hybrid/overlay rebo kolmogorov/crespi/z 14.0
pair_coeff     * * rebo                 CH.airebo  C C
pair_coeff     1 2 kolmogorov/crespi/z  CC.KC   C C

In this case, I can not use "pair_coeff     1*2 1*2 kolmogorov/crespi/z  CC.KC   C C" instead since it will change the interaction.
I know that the neighbor list is already built for types 1 1 in pair_airebo.cpp. My question is how to invoke this neighbor list in the new pair style I'm implementing?
Do you have any suggestion?
Thank you very much!

Best,
Ouyang

On Wed, Jul 26, 2017 at 6:26 PM, Axel Kohlmeyer <akohlmey@...24...> wrote:


On Wed, Jul 26, 2017 at 3:16 AM, ouyang <w.g.ouyang@...24...> wrote:
Hi all,
Recently I want to add the correct local normals to the Kolmogorov-Crespi (KC) potential based on the present version of KC potential (pair_kolmogorov_crespi_z.cpp) in USER-MISC package in LAMMPS. 
The present version of KC potential in LAMMPS assumes that all normals are along the z-axis, which leads this potential only valid for flat surfaces (e.g., not valid for carbon nanotubes). So I want to add the correct local normals to this KC potential.
When implementing the code, I met a problem. Assuming there are two layers of graphene with the atoms in the bottom layer setting to type 1 and the atoms in the top layer setting to type 2. This present KC potential is invoked in the input file like follows:
pair_style     hybrid/overlay kolmogorov/crespi/z 20.0
pair_coeff     * * none
pair_coeff     1 2 kolmogorov/crespi/z  CC.KC   C C
As a result, only the neighbor list between types 1 and 2 is built and there is no neighbor list built for the atoms within one layer (i.e., types 1 1 and types 2 2). Therefore, to calculate the local normals, I need to build a neighbor list for the atoms within one layer. I tried to build this neighbor list by introducing another cutoff but I failed.
Does anyone has an idea for how to build this neighbor list? Thank you in advance!

​please replace:

​pair_coeff     1 2 kolmogorov/crespi/z  CC.KC   C C

with:

pair_coeff     1*2 1*2 kolmogorov/crespi/z  CC.KC   C C

and the neighbor list handed to the kolmogorov/crespi/z calculation will contain all pairs you are asking for.
for details of the syntax, please see the documentation of the pair_coeff command.

axel.

 

Best,
Ouyang

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--
Dr. Axel Kohlmeyer  akohlmey@...24...  http://goo.gl/1wk0
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.