Unable to observe Insertion/Deletion in a GCMC simulation of xylene in zeolite

It looks like you have overlapping atoms in your zeolite configuration. You'll need to verify that your configuration doesn't include duplicate atoms on opposite faces of your simulation cell. If so, they will be wrapped by Cassandra such that they sit on top of each other and your energy will blow up.

Here are the steps I'd recommend for getting a toluene-in-zeolite simulation up and running:

(1) Run an NVT simulation of a single, toluene molecule. Confirm that the energies and configurations look reasonable.
(2) Run a GCMC simulation of a toluene gas. Confirm that you can insert and delete molecules in the gas phase (most moves should be accepted). Also, confirm that the chemical potential vs pressure look reasonable.
(3) Run a zero-step simulation of your zeolite configuration. Confirm that the energy looks reasonable.

Only after you successfully complete steps 1-3, should you attempt a GCMC simulation of toluene in the zeolite. We're happy to check in with you regarding your results after each step.