Calculation of free energies and chemical potentials for gas hydrates using Monte Carlo simulations
We describe a method for calculating free energies and chemical potentials for molecular models of gas hydrate systems using Monte Carlo simulations. The method has two components: (i) thermodynamic integration to obtain the water and guest molecule chemical potentials as functions of the hydrate oc...
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| Format: | Text |
| Language: | unknown |
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SelectedWorks
2007
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| Online Access: | https://works.bepress.com/peter_monson/3 https://works.bepress.com/cgi/viewcontent.cgi?article=1005&context=peter_monson |
| Summary: | We describe a method for calculating free energies and chemical potentials for molecular models of gas hydrate systems using Monte Carlo simulations. The method has two components: (i) thermodynamic integration to obtain the water and guest molecule chemical potentials as functions of the hydrate occupancy; (ii) calculation of the free energy of the zero-occupancy hydrate system using thermodynamic integration from an Einstein crystal reference state. The approach is applicable to any classical molecular model of a hydrate. We illustrate the methodology with an application to the structure-I methane hydrate using two molecular models. Results from the method are also used to assess approximations in the van der Waals−Platteeuw theory and some of its extensions. It is shown that the success of the van der Waals−Platteeuw theory is in part due to a cancellation of the error arising from the assumption of a fixed configuration of water molecules in the hydrate framework with that arising from the neglect of methane−methane interactions. |
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