Twisting of infinite CNT using periodic boundary conditions

LAMMPS LAMMPS General Discussion
1

Hi,

Is it possible to implement twisting or bending of infinite CNT using the periodic boundary conditions on LAMMPS?

Thanks.

2

That cannot work by the nature of the geometry of (3d) periodic boundaries.

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3

Since electrostatics are not so crucial in the description of CNT, why don’t you just drop periodic boundary conditions? Freeze the tips of the nanotube and you are good to go.

4

The same thing can also be done with PBC, just define two small regions with equal distance to each other in either direction and define a group for each and the rest of the atoms. Then apply fix move on the two small groups with rotations ( one clockwise, the other counterclockwise) and you will have a readily twisting “infinite” CNT. The same can be done with bending, provided the box is large enough (or you use shrinkwrap boundaries), but beware that this will also strain the CNT.

5

I am not sure if this procedure is equivalent to twisting of an “infinite” CNT. Beacuse, as soon as we apply twist the translational symmetry is lost. Maybe i am missing something. Could you elaborate your point further? Here’s a relevant paper that might be useful.

6

No. This is about your research and not about LAMMPS anymore. I can describe the “mechanical” parts of how you can do something with LAMMPS (and that is what I did), but whether that is applicable to your research is not something I am interested in or care to discuss. In fact, I would consider this off-topic for this section of this forum. Usually, the science is something you have to discuss with your adviser.

The matter of the fact remains: what you are asking for is not compatible with periodic boundaries in 3 or 2 dimensions and would require significant C++ programming to be implemented in 1 dimension. What I have described is the closest you can do with the existing LAMMPS code.

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