(a) Relationship between the hydrate equilibrium pressures and van der Waals diameter of the guest compounds. (b) Relationship between the hydrate equilibrium pressures and molar mass of the guest compounds. Squares and circles indicate the data for the type-I and type-II hydrates, respectively. Equilibrium-pressure data at the temperature of are used (Ref. 10). van der Waals diameters were calculated with Winmostar (Refs. 11 and 12) The chemical formulas in the figure indicate the guest compounds.
Schematic illustration of the cages forming (a) type-I and (b) type-II hydrates.
Contour map of the residual free energy for (a) type-I and (b) type-II hydrates. The and of the molecules in Table II are also plotted.
Contour map of the residual free energy for each cavity; (a) large cavity and (b) small cavity of the type-I and (c) large cavity and (d) small cavity of the type-II hydrates.
The dependency of the residual free energy on for each cage and the whole hydrate at .
Arrangement of the guest-molecule sizes and optimal sizes of for each type of cage and hydrate.
Combinations of , , , and of the guest molecules used for the calculations of the free energy differences between systems and .
The Lennard-Jones parameters and of , , Xe, , , Kr, , Ar, Ne, and He. They were compared with the maximum van der Waals (vdW) diameters.
The calculated free energy differences between the hydrates formed with Xe, Kr, , , Ar, , , , Ne, and He and for the type-I and type-II hydrates. The hydrate is employed as a reference to calculate the free energy differences. The unit is .
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