How to set two ellipsoid particles as rigid

Dear lammps-users,

I want to set two ellipsoid particles as rigid, that is, a rigid molecule consisting of two ellipsoid particles. How can I implement such a function in LAMMPS? Which command ?

Dongbo Wang

Have you checked the LAMMPS documentation? That is what it is for!

If I already found the answer in the manual, I will not ask again here. I have checked the LAMMPS documentation, but I have not found useful information about my question. It could be that I didn’t look in the right place. Could you give me some suggestions about which section of documentation can I find the answer to that question?

Have you tried the search box?

Of course, the LAMMPS manual is 2000 pages long! Do I have to go through it carefully page by page?

If you type “rigid” into it, then it will reveal “fix rigid” among the answers. Did you read that doc page?

Just reading through the pages that are indicated by the search should reduce it to a manageable amount.

Okay, thank you very much for your response. However, I don’t think that fix rigid can help achieve what I need in my simulation. In fact, I will perform simulations of tens of thousands of ellipsoidal particles, consisting of two types of particles A and B, and I need to bind each A and B particle together to form a molecule A-B in the initial model. This means that I would need to identify each particle as an atom group, which I think is not feasible. Can the fix rigid command achieve this function in a more convenient way?

I am confused by this question because the very documentation page, I pointed out, has a detailed discussion of both, various methods for how to assemble atoms into rigid bodies, and for which scenario which rigid style variant is more appropriate including the case of many small rigid objects. What else do you need?

If you expect a do this, not that kind of tutorial where every detail specific to your case is spelled out, then you are in the wrong business. Any large, modular, and flexible software package like LAMMPS comes with a some assembly required™ sticker attached to it.