GCMC for guest adsorption in porous materials

GULP
1

Dear Prof. Gale, I hope you are doing well.

I was testing GCMC simulations in GULP to estimate guest uptake in a porous material. Out of curiosity, I also tried the pGFN-FF model and was able to set up an initial input. However, when using the conv option, the MC moves are also applied to the framework atoms.

To keep the framework rigid, I froze all framework atoms using the three flags after their coordinates, but in that case the guests are often inserted too close to the material.

I have tested He and H2 as probe particles and several chemical potentials, trying to insert only a few guests, but the accepted configurations still show very short contacts. I am unsure whether this indicates a limitation of the model, a problem in how I am fixing the framework atoms, or something else.

So, my questions are: 1) is pGFN-FF intended to be used for GCMC simulations in GULP, and 2) is freezing the framework atoms with the coordinate flags the correct approach for rigid-framework GCMC simulations?

I have carefully reviewed the MC options in the manual, but I may be missing something here.

Best regards

2

Dear Alexa,

Sorry for the delayed response. Here are answers to your questions:

  1. The pGFN-FF model isn’t well suited to GCMC I’m afraid. This is because it computes connectivity and parameters on the fly & so the energy isn’t going to be well behaved for a system where atoms are inserted or removed, especially if a trial move places them in a site where they might bond to the framework.

  2. If you want to perform a rigid framework simulation then you’ve done the right thing - remove “conv” and set the flags so that the framework atoms are fixed.

Best regards,

Julian

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