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Re: [lammps-users] force calculation in tersoff potential
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Re: [lammps-users] force calculation in tersoff potential

From: Axel Kohlmeyer <akohlmey@...24...>
Date: Sat, 25 Nov 2017 15:03:34 -0500

On Sat, Nov 25, 2017 at 9:59 AM, Nader Ameli <nader.mechanic@...24...> wrote:

Dear LAMMPS users,

I am using “Tersoff” pair style for nanometric machining and want to calculate force between tool and workpiece groups. According LAMMPS manual, we could not use compute group/group. Hence, I used variable fcm command as bellow:


variable forcex equal fcm(tool,x)

variable forcey equal fcm(tool,y)

variable forcez equal fcm(tool,z)

fix        12        mobile print 50 "${forcex}" file TotalFeatures/forcex  screen no

fix        13        mobile print 50 "${forcey}" file TotalFeatures/forcey screen no

fix        14        mobile print 50 "${forcez}" file TotalFeatures/forcez screen no


In this regard, I have 2 questions:

1- The achieved forces from these commands are 0.0 during the process. Why is that? I made my tool rigid. Could it be the reason of this?

2- Logically, forces on tool should be equal with the forces on workpiece. Nevertheless, when I put workpiece group in my variable fcm command, the result has been changed and showed a very bad fluctuation:

variable forcex equal fcm(workpiece,x)


Could you please help me in this issue?

​there is not enough information provided to give any kind of meaningful help.




Best Regards


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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.