[lammps-users] (no subject)

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1

Hi
I use “fix smd” to draw graphene but the force it gives in the X direction is negative ,I write the code as follows:

fix 1 graphene smd cvel 20.0 0.001 tether 100.0 NULL NULL 0.0

How can I get positive force?

Is the first component of “fix smd” related to the pulling force?

Thanks for the reply.

2
  • you are still not using a descriptive subject; some people consider this impolite; it will certainly hurt your chances to attract people to read your message and provide a response
  • you have as of yet failed to explain what you understand as “pulling force”
  • the sign of the force is an indication of its direction with respect to the geometry and the pulling direction. why “must” it be positive? unless there is a particular strong retention or expulsion I would expect the sign of the force to fluctuate over an steered MD run. Details on that can be found in the publications describing steered MD and how to properly analyze it and tune its settings for accurate results.
  • what LAMMPS computes is described in the documentation; how this relates to what you want to compute is your task to figure out, especially since you persistently avoid to explain what exactly you are looking for