NpT Gibbs Ensemble: Fixing the Volume of Certain Box?

[kliu]

Dear Professor Dubbeldam,

I am trying to do NpT Gibbs Ensemble Monte Carlo simulation instead of NVT Gibbs Ensemble simulation (total volume of the two boxes fixed). For our research problem, we are eventually trying to run the two boxes at different conditions to simulate adsorption process in hopes of following Professor Ilja Siepmann's group's procedure. We hope to run a direct simulation of mixture adsorption.

I could not find an example of running NpT Gibbe Ensemble simulation from the manual, so I proposed that for an NpT Gibbs Ensemble simulation that both boxes are allowed to grow, I can combine NpT ensemble (to utilize the keyword VolumeChangeProbability) with GibbsSwapProbability (imposing chemical equilibrium). The volume change is controlled by the keyword VolumeChangeProbability. Do you agree with such algorithm, or there is a better way to do this type of Gibbs Ensemble?

Following the question above, we want to simulate the case where one box has its volume fixed. Is there a way in Raspa to do this?

Thank you very much for your time and help.

Best,
Kunhuan

[David Dubbeldam]

In RASPA, the ensemble follows from the MC-moves.
So for NPT Gibbs you would use:
1) VolumeChangeProbability
2) GibbsSwapProbability
3) GibbsIdentityChangeProbability (assuming you have more than one component, otherwise you would use NVT-Gibbs).
4) thermalization moves like TranslationProbability, RotationProbability, ReinsertionProbability etc.

So the difference between NVT-Gibbs and NPT-Gibbs is that NVT-Gibbs uses a special volume move 'GibbsVolumeChangeProbability' so that the total volume is fixed. NPT-Gibbs uses the normal volume 'VolumeChangeProbability' that adjust each simulation box according to the specified pressure.