Calamitic and antinematic orientational order produced by the generalized Straley lattice model

Bisi, Fulvio, De Matteis, Giovanni and Romano, Silvano (2013) Calamitic and antinematic orientational order produced by the generalized Straley lattice model. Physical Review E, 88 (3). 032502. ISSN 1539-3755

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We consider here a classical model, consisting of D2h-symmetric particles in a three-dimensional simple-cubic lattice; the pair potential is isotropic in orientation space, and restricted to nearest neighbors. The simplest potential model is written in terms of the squares of the scalar products between unit vectors describing the three interacting arms of the molecules, as proposed in previous literature. Two predominant antinematic couplings of equal strength (+1) are perturbed by a comparatively weaker calamitic one, parameterized by a coupling constant −z ranging in [−1,0]. This choice rules out thermodynamically stable phases endowed with macroscopic biaxiality. The antinematic terms favor states with the corresponding molecular axes mutually orthogonal. Although the low-temperature phase of the special case with null calamitic term (PP0) is uniaxial and antinematically ordered, in the general case presented here both Monte Carlo and molecular-field approaches show that, for z close to zero, the models exhibit a low-temperature uniaxial nematic phase, followed by an antinematic one, and finally by the orientationally disordered one. On the other hand, for sufficiently large values of z, we only find evidence of uniaxial calamitic behavior, as expected by following the limiting cases.

Item Type: Article
Subjects: G100 Mathematics
G300 Statistics
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: Ellen Cole
Date Deposited: 10 Oct 2013 08:26
Last Modified: 13 Oct 2019 00:33

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