I want to see how small particles will detach from the larger objects (eg detachment of powder from coated balls), But I cannot understand how the particles will be attached to rum simulation in the first place. How to add vander walls force in LAMMPS?
From your questions it seems that you need help from an advisor or anybody experienced with simulations near you.
To answer your questions specifically, you can find all the interaction potentials implemented in LAMMPS in the documentation (https://docs.lammps.org). Then it is up to you to choose which one fits your system. “How the particle” will detach will depend on the configuration you choose in the first place, I suggest to find inspiration in the literature for that, and then try to reproduce what they do.