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Solution of an associating lattice gas model with density anomaly on a Husimi lattice | | T. J. Oliveira
; J. F. Stilck
; M. A. A. Barbosa
; | | Date: |
10 Dec 2009 | | Abstract: | We study a lattice gas model with orientational degrees of freedom, which is
the simplified version of the Henriques-Barbosa model, no distinction is made
between donors and acceptors in the bonding arms. We solve the model in the
grand-canonical ensemble on a Husimi lattice built with hexagonal plaquettes
with a central site. The ground-state of the model, which was originally
defined on the triangular lattice, is exactly reproduced by the solution on
this Husimi lattice. In the phase diagram, one gas and two liquid (high
density-HDL and low density-LDL) phases are present. All phase transitions
(GAS-LDL, GAS-HDL, and LDL-HDL) are discontinuous, and the three phases coexist
at a triple point. A line of temperatures of maximum density (TMD) in the
isobars is found in the metastable GAS phase, as well as another line of
temperatures of minimum density (TmD) appears in the LDL phase, part of it in
the stable region and another in the metastable region of this phase. These
findings are at variance with simulational results for the same model on the
triangular lattice, which suggested a phase diagram with two critical points.
However, our results show very good quantitative agreement with the
simulations, both for the coexistence loci and the densities of particles and
of hydrogen bonds. Finally, we consider the same model if homogeneity of the
configurations is assumed, and show that a qualitatively different phase
diagram is found, with a single liquid and a gas phase. Although again a TMD is
present in the homogeneous case, it is located in a part of the diagram with
negative entropy, thus providing additional evidence for the recent findings
that requiring homogeneity in such models may lead to unphysical results. | | Source: | arXiv, 0912.2062 | | Services: | Forum | Review | PDF | Favorites | |
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