Hi, i write a data file for single molecule of triethylene glycol, how can i turn it to a bunch of molecules like a fluid? How many molecules need to do it?
Thank you
you can “grow” your system using the “replicate” command. if you want to turn this into a fluid, you will likely need to shrink the box (e.g. with change_box to be reasonably close to the desired density, and then through equilibration - first with fix nve + langevin, then with fix npt - until it is reaches a reasonable degree of equilibration.
how large this system would need to be depends on your application and what kind of property you are looking for. there is no general rule outside of: you need to grow your system until finite size effects become small enough to have no significant impact on what you want to find out from your simulations.
There are, of course, other approaches and tools. Some of those are listed here: https://lammps.sandia.gov/prepost.html
Since this is not a LAMMPS specific topic, you can look up how people set up build fluids in tutorials or text books on general MD methodology or other MD codes.
Axel.