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Phase diagram of model anisotropic particles with octahedral symmetry
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Image of FIG. 1.
FIG. 1.

A schematic representation of the geometry of the interaction between two particles. For clarity, we depict a two-dimensional analog of the three-dimensional model used in this work. In this two-dimensional model, the particles have four patches arranged regularly with their directions described by the patch vectors, . In the particular case shown in the figure, patch 4 on particle interacts with patch 2 on particle because they are the closest to the interparticle vector.

Image of FIG. 2.
FIG. 2.

(Color online) Unit cells of the (a) bcc and (b) orientationally ordered fcc-o structures. In both cases the patches are aligned with the second neighbors.

Image of FIG. 3.
FIG. 3.

Determination of the coexistence point between the fluid (solid line) and the bcc (dashed line) phases at .

Image of FIG. 4.
FIG. 4.

(Color) The variation of the internal energy per particle during simulations of a box containing the bcc solid in contact with the fluid at . A few trajectories at different temperatures are shown.

Image of FIG. 5.
FIG. 5.

(Color) (a) Snapshot of the initial configuration of the simulation box containing the bcc and the fluid phases in contact. (b) and (c) Snapshots of the final configurations for and , respectively. The pressure was set to .

Image of FIG. 6.
FIG. 6.

Dependence of the vapor-liquid coexistence curve on the patch width . At lower we were unable to find the (metastable) coexistence curves.

Image of FIG. 7.
FIG. 7.

phase diagram of our octahedral six-patch particle system (with ). Labels show the region of stability of each phase. The points at which the reentrant behavior occurs are indicated with a cross.

Image of FIG. 8.
FIG. 8.

phase diagram of the octahedral six-patch particle system (with ). Labels show the region of stability of each phase. The reentrant behavior occurs at the points at which there is a change of sign in the slope of the phase boundaries. These points are indicated by a cross. The black circle shows the point where inverse melting occurs.

Image of FIG. 9.
FIG. 9.

(Color online) Detailed view of the phase diagram in the region of the sc-liquid-bcc triple point. The triple point is shown with a dashed line. Labels indicate the region of stability of each phase. The point at which reentrant behavior occurs is indicated by a cross.

Image of FIG. 10.
FIG. 10.

Equation of state for the liquid phase (circles) and the sc crystal (asterisks) at .


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Table I.

Coefficients obtained by fitting the integrand of Eq. (5) to a polynomial of degree six [Eq. (14)].

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Table II.

Free energy of the solid phases, as obtained by thermodynamic integration from the Einstein crystal. The free energies (, , and ) and the lattice energy are given in units of .

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Table III.

Coefficients of the polynomial fit to the equation of state of the solid phases. The points were fitted to a third-degree polynomial, except for the bcc structure at , for which a fourth-degree polynomial significantly improves the fit.

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Table IV.

Coexistence points obtained using the thermodynamic integration method. The points marked with an asterisk were used as the starting points for the Gibbs–Duhem approach. The other points served to test our calculations.

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Table V.

Melting points obtained using the direct coexistence method. For comparison, the coexistence points obtained from the free energy calculations (see Table IV) are also shown. Note that the sc-fluid coexistence point was obtained using the Gibbs-Duhem method (see Table VI).

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Table VI.

Some of the coexistence points obtained with the Gibbs–Duhem method.

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Table VII.

Thermodynamic states for the two triple points in the phase diagram.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Phase diagram of model anisotropic particles with octahedral symmetry