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Re: [lammps-users] How about Interaction potential in a binary system?
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Re: [lammps-users] How about Interaction potential in a binary system?

From: Xiaolin Xu <xiaolin.xu2@...24...>
Date: Sun, 20 May 2018 23:25:25 +1000

Thanks very much Dr. Axel for your nice explanations. I appreciate your time.
Luckily, for my case, an alloy is not formed.

May I know what you exactly mean by ""generic" lj/cut force field parameters" ? Do you mean determining sigma and epsilon parameters of the LJ potential using DFT calculations?


On Sun, May 20, 2018 at 11:06 PM, Axel Kohlmeyer <akohlmey@...29....> wrote:

On Sun, May 20, 2018 at 7:01 AM, Xiaolin Xu <xiaolin.xu2@...92......> wrote:

I want to investigate systems such as Al-Si. I have the eam potential file for Al, and tersoff for Si (Al-Al and Si-Si are thus available). Therefore, a hybrid pair-style can be used. However, I do not have the interaction potential between Al and Si.

​you are missing one very important step in your logic. if you have an Al-Si alloy, you *should* not use ​a hybrid pair style. both, EAM and Tersoff have force terms that depend not only on the individual pairs, but also on neighboring atoms. those will be missing with a hybrid pair style and thus you are running a high risk of producing a garbage simulation unless you have a separate Al area and an Si area and only a rather small contact area, where you can use a pair-wise additive potential (e.g. lj/cut) as an approximation for the inter-style interaction. for "machining" or "impact" simulations, where mostly the repulsive cross interactions matter, this is a reasonable approximation.

What options I have, and what solutions lammps presents to the users in such cases? 

​if your case matches, the scenario described above, you can look up "generic" lj/cut force field parameters and move on. for pretty much any other scenario, you *need* to find a potential/force field set of parameters from the literature, that covers your *entire* system. pair style hybrid would result in too large a systematical error.

please keep in mind, that LAMMPS primarily provides the functional form. there are far too many parameter sets available to bundle them all with LAMMPS.




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