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Free-energy calculation of structure-H hydrates
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Image of FIG. 1.
FIG. 1.

A histogram of the dipole moment of a structure-H unit cell. The axis is scaled by the dipole moment of TIP4P water.

Image of FIG. 2.
FIG. 2.

A histogram of the net potential energy of the structure-H unit cell.

Image of FIG. 3.
FIG. 3.

Potential energy and net dipole moment of the structure-H unit cells randomly selected from cells.

Image of FIG. 4.
FIG. 4.

A snapshot of the simulation cell used for the structure-H hydrate at and with and . The dark circles represent the LMGS molecules, the light circles represent the methane molecules, and the rods represent the hydrogen bonds. The water molecules have not been shown here.

Image of FIG. 5.
FIG. 5.

Radial distribution functions (RDFs) of (a) water-water molecules, (b) water-guest and water-LMGS molecules, (c) guest-LMGS molecules, and (d) LMGS-LMGS molecules at and .

Image of FIG. 6.
FIG. 6.

RDFs of the (a) LMGS-LMGS, (b) LMGS-oxygen of water molecules, and (c) LMGS-methane molecules at and and .

Image of FIG. 7.
FIG. 7.

of the LMGS molcules at and and .

Image of FIG. 8.
FIG. 8.

Dependence of on and . (a) was fixed at and (b) was fixed at . Both lines correspond to those of the fourth-order polynomials obtained by the least-squares method.

Image of FIG. 9.
FIG. 9.

Dependence of the free energy on . (a) was fixed at and (b) was fixed at . These lines correspond to those of the fifth-order polynomials, which are obtained by integrating the fourth-order polynomials estimated earlier.

Image of FIG. 10.
FIG. 10.

Dependence of , , , and on .

Image of FIG. 11.
FIG. 11.

Contours of the free-energy difference at (a) , (b) , and (c) . and pairs of the LMGS molecules listed in Table I are also plotted.

Image of FIG. 12.
FIG. 12.

Plots of against (a) , (b) , and (c) at different values of at .


Generic image for table
Generic image for table
Table I.

A list of the LMGS molecules with the LJ parameters of the one-site model (Ref. 19). These LJ parameters determined by the viscosity and second virial coefficient are accurately reproduced.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Free-energy calculation of structure-H hydrates