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Re: [lammps-users] Question about Pair Coeff for Beads of same atoms types
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Re: [lammps-users] Question about Pair Coeff for Beads of same atoms types

From: Axel Kohlmeyer <akohlmey@...24...>
Date: Fri, 23 Jun 2017 17:25:48 -0400

On Fri, Jun 23, 2017 at 4:07 PM, George Ray <uraykol12@...24...> wrote:
Hello everyone,

I am using Lammps 14May-2016 version. I will describe my system first before asking my question. Basically it is a bead spring model. I have 4 beads to make up one chain. And there are many chains arranged together in a bundle. All the beads are of the same atom type and have the same mass.

Besides the harmonic bond style, angle style and dihedral styles, there are lj 6-12 potential fit between each beads in a chain and a lj 9-6 potential between beads in the adjacent chains.

Now my question is by specifying a command like "pair_coeff 1 1 100.0 3.5 9.0" , I can specify the interactions between beads in each of the chains. However what do I do for capturing the lj 9/6 potential which is basically between chains?

I thought of one solution. I can change the atom types in each chain and modify the data file. For example, if there are 8 chains I can have atom types 1-8. The lj9/6 can be captured by using something like the "pair_coeff 1 2 100.0 3.5 9.0" and so on. However, the problem is if I have many chains (around 50), it is very tedious to capture each cross term pair_Coeff command.  Is there a better way for this? Any feedback will be much appreciated.

please check, if i ​do understand you correctly​:
- a "molecule" would be a 4-bead chain
- the 12-6 LJ terms are only for *intra*molecular pairs
- the 9-6 LJ terms are only for *inter*molecular pairs
- you are currently using special_bonds lj/coul 1.0 1.0 1.0

if yes, i may have a suggestion for you.
if no, please try explaining again



Thank you so much for your help.


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Dr. Axel Kohlmeyer  akohlmey@...12...24...
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.