Inducing flow in SRD fluid + big particles

Dear lammps users,

I am trying to simulate a system of big particles embedded in a fluid of srd particles.

I would like to add an external force on srd particles. I have followed the thread and compiled the modified version of fix_srd (attached therein), in order to implement the external force on srd particles.

My problem is that I have a constant number of srd particles inside big particles. I generate the initial configuration by randomly positioning the colloids and the srd particles. As you can see from the attached in.srd file, I perform the fix nve/limit command to partially remove the overlap. When I start the simulation run I have around 1000 srd particles inside big particles, and this number does not go to zero with increasing simulation time, on the contrary it oscillates about 1000. However, If I use the stable version of lammps 16Mar2018, the number of srd particles inside big particles decreases with simulation time, eventually becoming zero. I wonder why this does not occur with the modified version of fix_srd. I exclude the possibility that the external force might cause this problem because I verified that by setting the external force on srd particles equal to zero I still obtain 1000 srd particle inside big particles.

Thank you in advance.

Kind regards,

Giulia Fiorucci

in.srd (2.57 KB)

You should not start with SRD particles inside big particles. You can use delete_atoms overlap
to remove them before you start the first run. If you get overlaps
after that, it could be b/c you are using a modified fix srd (not part of LAMMPS).
I don’t believe normal fix srd should allow for overlaps.