How to Create a Spherical Janus Particles

Dear All,
      I'm trying to perform a simulation involving a spherical Janus
particle, But I don't have much idea about creating a Janus particle
in Lammps. Can anybody help me with this..

Thanks in Advance

-Praveen

Your best bet is to find some publications on simulations involving Janus particles (there are many) similar to what you want to do and trying to implement their model in LAMMPS. The level of detail of your model particle will depend on what you wish to learn from it and hence there is no one correct answer.

I’m trying to perform a simulation involving a spherical Janus
particle, But I don’t have much idea about creating a Janus particle
in Lammps. Can anybody help me with this.

I agree with what Stephan said.

…Nevertheless, for what it’s worth, here are two suggestions. I don’t know if either of them are relevant to what you are trying to do:

In the past, I simulated something similar using two spherical particles of different type (but the same size) separated by a small distance. (The separation distance was siginifantly smaller than width of each particle. If the particles are close enough together, the resulting object is approximately spherical.) The two sides can be tuned to be attracted to different kinds of particles. (…using the “pair_coeff” command)

If you try this method, I suggest using a strong spring (or “fix shake”) to keep the two particles separated by a fixed distance. If you’re not using “fix shake” the, depending on what pair style you are using, you probably also should use the “special_bonds” command to eliminate the strong repulsive forces between the two atoms that would likely occur as a result of their close proximity.

  1. Alternatively, you could create a “disco-ball”, a spherical shell made of smaller spheres. The spheres on one side of the ball could be of one type, and the spheres on the other side of the ball would be of a different type. Then hold the entire structure rigid using “fix rigid”. You can use google to search for code that will generate the XYZ coordinates for a “disco ball” shaped structure. This approach is slower because it requires many particles per Janus particle, and is a little more difficult because it requires “fix rigid” (which can be tricky to use at constant pressure). However if you use method 2, the attraction to one side of the Janus particle can be made to be approximately uniform over it’s surface.

Either of these approaches (1 or 2) requires creating a DATA file. You can either create one of these files yourself. The format is explained here:
https://lammps.sandia.gov/doc/2001/data_format.html

…Or you can use one of the molecule builders listed at
https://lammps.sandia.gov/prepost.html

(In that case, I recommend either moltemplate or topotools. Disclaimer: I wrote one of these tools. Both are designed for coarse grained models and both give you a great deal of control how to build your system.)

I hope something I said here was helpful.

Andrew

Your best bet is to find some publications on simulations involving Janus particles (there are many) similar to what you want to do and trying to implement their model in LAMMPS. The level of detail of your model particle will depend on what you wish to learn from it and hence there is no one correct answer.

True.