Chemical Potential in Gibbs Ensemble Monte Carlo
- jdmoore
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7 years 6 months ago #247
by ejmaginn
Josh,
We don't have an automatic method for computing chemical potentials in the two phases implemented. You could do this "outside" of the code using the method Smit outlines in his 1989 Molecular Physics paper. It is a modified Widom insertion method. You can also compute this from tracking the "Rosenbluth weights" during swaps, but we also do not do this. Regardless of whether it is shifted or not, what you want to see is that the value you get is equal between the two phases. It is really just a check of equilibrium. This is something we can add to our ever-expanding to-do list. Do you need the chemical potential for some other reason than just checking on equilibration?
Ed
We don't have an automatic method for computing chemical potentials in the two phases implemented. You could do this "outside" of the code using the method Smit outlines in his 1989 Molecular Physics paper. It is a modified Widom insertion method. You can also compute this from tracking the "Rosenbluth weights" during swaps, but we also do not do this. Regardless of whether it is shifted or not, what you want to see is that the value you get is equal between the two phases. It is really just a check of equilibrium. This is something we can add to our ever-expanding to-do list. Do you need the chemical potential for some other reason than just checking on equilibration?
Ed
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7 years 6 months ago #250
by jdmoore
Dear Dr. Maginn,
Thank you for your reply. I was just looking at Smit's 1989 paper, so it's good to hear I am on the right track.
I wanted to be able to use the chemical potentials as input to GCMC simulations, and I thought I could get those from GEMC for the VLE.
In the workshop materials, adsorption_slides.pdf from June 9th, Prof. Romanielo on page 27 gives several sets of chemical potentials for mixtures of CO2/CH4. How were these determined? I thought maybe she assumed an ideal mixture from the previous slide, but they appear to be slightly non-ideal. Did she run gas phase NPT MC simulations and then match these against a series of GCMC simulations fixing one chemical potential and varying the other until she found the point where Ptotal = 1 atm?
Thanks.
Josh
Thank you for your reply. I was just looking at Smit's 1989 paper, so it's good to hear I am on the right track.
I wanted to be able to use the chemical potentials as input to GCMC simulations, and I thought I could get those from GEMC for the VLE.
In the workshop materials, adsorption_slides.pdf from June 9th, Prof. Romanielo on page 27 gives several sets of chemical potentials for mixtures of CO2/CH4. How were these determined? I thought maybe she assumed an ideal mixture from the previous slide, but they appear to be slightly non-ideal. Did she run gas phase NPT MC simulations and then match these against a series of GCMC simulations fixing one chemical potential and varying the other until she found the point where Ptotal = 1 atm?
Thanks.
Josh
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