How to make a cylindrical model by Lammps?

LAMMPS LAMMPS General Discussion
1

Dear experts,

I am going to make a cylindrical model in Lammps by melt-quenching method.

When I make a block model and reduce the atoms by the “delete_atoms” command and get a cylindrical shape, the boundaries of the simulation cell do not coincide with the walls of the cylindrical model and in the best case they are tangent to its walls.

Is there a way for me to create a cylindrical model so that the boundaries of the simulation cell coincide with the walls of the model (the boundaries of the simulation cell have curves like the walls of the cylindrical model)?

Best regards,

Akram

2

Why not start from a cylinder region directly?

No. How should that work physically?

You cannot have periodic boundaries in x-, and y- for a cylinder along the z-axis, or equivalent.

So the only available options are to have either a free surface (which requires fixed or shrinkwrap boundaries or sufficient vacuum between periodic images) or to use a confinement potential via fix wall/region.

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3

Thank you very much for your reply
I can’t start with an initial cylindrical model because I am going to make an amorphous sample that first melts and after equilibration at high temperature, it is quenched and I doubt that its cylindrical shape will be preserved! Am I thinking wrong?

4

Why not use a confinement potential?

5

This is easy to answer by just setting up a small test input and try it out.

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6

After reviewing the Lammps manual, I intended to use the “fix wall/region command”, but I did not have the correct information to determine its style (style = lj93 or lj126 or lj1043 or colloid or harmonic or morse) and arguments(epsilon/sigma).
My amorphous alloy sample consists of 3 metals and its potential is “EAM”.

8

For confinement it is usually best to use a harmonic wall, since that is repulsive only.

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9

Thank you very much. I appreciate the help you gave me and will definitely try the methods you mentioned