Monte Carlo Simulation of Polymers

I am trying to do a simple Monte Carlo Simulation of a polymer without insertions or deletions. To achieve this, I use the fix gcmc command and set the average number of GCMC exchanges to attempt every N steps to 0. I am able to run the simulation sucessfully. However the simulation runs too slow.

I have a polymer with 500 monomers, with harmonic bonds and WCA pair potential. Each iteration takes almost 2 seconds. Is there any way I could speed this up?

This is my exact command -

fix mc myatoms gcmc 1 0 500 1 ${seed} 1.0 0 0.2 mcmoves 1 0 0 full_energy

This is expected behavior. For each MC move you need to do a force force computation across all particles with the full_energy option, so that is highly ineffective. Fix gcmc was not intended for this kind of use mode, but rather for adding occasional MC moves to an MD simulation in order to speed up slow processes like diffusion through zeolite systems.

Please keep in mind that LAMMPS is a molecular dynamics code and its usefulness for pure MC is very limited unless you would program an efficient MC engine with specialized steps to speed up certain time consuming steps.