Assistance with Drift and Torsion in Cantilever Simulation

LAMMPS LAMMPS General Discussion
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1

Dear LAMMPS Experts,

I am modeling a 3D cantilever in LAMMPS with a slab geometry. However, I am encountering an issue with drift movement, or more specifically, torsion, observed in the cantilever, particularly near its free tip after minimization.

To address this, I attempted to use the fix momentum command immediately after minimization and before applying a load to the tip using fix addforce, but this approach was unsuccessful. I also tried increasing the duration for which fix momentum is applied and experimented with adjusting its frequency, but neither resolved the issue.

I suspect the problem might be related to the reflective walls I have defined for the simulation box, though I am not entirely certain.

I would greatly appreciate any comments, suggestions, or insights you may have to help resolve this issue.

Attached, you will find the input file and an image illustrating the observed drift at the cantilever tip: one edge moves upward while the other moves downward, whereas both edges should ideally move uniformly together.

Thank you in advance for your assistance.

Best regards,
Bahman

Attachments:

Desktop_image_2
Desktop_image_21089×400 201 KB

In.cantilever (4.8 KB)
Si.tersoff.Si (430 Bytes)

2

Why do you say that this an issue ? Isn’t it just a physical motion of your system ?

If you want to keep the system from deforming, then you should use commands like fix spring/self, but not fix momentum.

3

Thanks for your response. But it did not work too. It seems that the torque caused by using fix addforce instead of fix aveforce on the tip of the cantilever. Now, I am going to read more about difference between fix addforce and fix aveforce.