Monte Carlo study with reweighting of uniaxial nematic liquid crystals composed of biaxial molecules.

We present a high accuracy Monte Carlo simulation study of the uniaxial nematic (N_{U}) to isotropic (I) phase transition of a lattice dispersion model of uniaxial nematics composed of biaxial molecules. The N_{U}-I coexistence curve terminating at the Landau critical point has been determined using the multiple histogram reweighting technique. A close investigation reveals a sharp departure in the nature of the N_{U}-I coexistence curve in the temperature-biaxiality parameter phase diagram in comparison to the earlier theoretical (either mean-field or computer simulation) predictions.

Pressure-induced phase transitions in liquid crystals: A molecular field approach.

A rigorous microscopic treatment of a nematic fluid system based on a pairwise interaction potential is immensely complex. For studying such systems molecular field theories are often the standard method of choice. In this paper we have chosen a simple effective potential U=u_{4}/v^{4}-u_{2}/v^{2}-Au_{2}/v^{2}〈P_{2}〉P_{2}(cosϑ) to study an isothermal-isobaric ensemble describing a liquid crystalline system.

Monte Carlo investigation of critical properties of the Landau point of a biaxial liquid-crystal system.

Extensive Monte Carlo simulations are performed to investigate the critical properties of a special singular point usually known as the Landau point. The singular behavior is studied in the case when the order parameter is a tensor of rank 2. Such an order parameter is associated with a nematic-liquid-crystal phase.

Effect of an external magnetic field on the nematic-isotropic phase transition in mesogenic systems of uniaxial and biaxial molecules: a Monte Carlo study.

We determine the nematic-isotropic coexistence curve terminating at the critical point in a temperature-external field phase diagram for nematic liquid crystals with positive diamagnetic anisotropy, where the molecules are either perfectly uniaxial or biaxial using computer simulation of a lattice model. The coexistence curve is much steeper than that predicted by the standard Landau-de Gennes and Maier-Saupe mean-field theories. For the uniaxial system the critical magnetic field is estimated to be one order of magnitude lower than the mean-field estimate but of the same order of magnitude as the experimental measurement.

Local and global persistence exponents of two quenched continuous-lattice spin models.

Local and global persistence exponents associated with zero-temperature quenched dynamics of two-dimensional XY model and three-dimensional Heisenberg model have been estimated using numerical simulations. The method of block persistence has been used to find the global and local exponents simultaneously (in a single simulation). Temperature universality of both the exponents for three-dimensional Heisenberg model has been confirmed by simulating the stochastic (with noise) version of the equation of motion.

Role of topological defects in the phase transition of a modified XY model: a Monte Carlo study.

Monte Carlo simulation has been performed on a classical two-dimensional XY model with a modified form of interaction potential to investigate the role of topological defects on the phase transition exhibited by the model. In simulations in a restricted ensemble without defects, the system appears to remain ordered at all temperatures. Suppression of topological defects on the square plaquettes in the modified XY model leads to complete elimination of the phase transition observed in this model.

Finite size scaling and first-order phase transition in a modified XY model.

Monte Carlo simulation has been performed in a two-dimensional modified XY -model first proposed by Domany [Phys. Rev. Lett.

Dynamical scaling in two-dimensional quenched uniaxial nematic liquid crystals.

The phase-ordering kinetics of the two-dimensional uniaxial nematic has been studied using a cell dynamic scheme. The system after quench from T=infinity was found to scale dynamically with an asymptotic growth law similar to that of the two-dimensional O(2) model (quenched from above the Kosterlitz-Thouless transition temperature), i.e.

Phase transitions in two planar lattice models and topological defects: a Monte Carlo study.

Monte Carlo simulation has been performed in the planar P2 and P4 models to investigate the effects of the suppression of topological defects on the phase transition exhibited by these models. Suppression of the 1/2 defects on the square plaquettes in the P2 model leads to complete elimination of the phase transition observed in this model. However, in the P4 model, on suppressing the single 1/2 defects on square plaquettes, the otherwise first order phase transition changes to a second order one which occurs at a higher temperature, and this is due to the presence of a large number of 1/2 pair defects which are left within the square plaquettes.

Monte Carlo simulation of the nematic-isotropic transition in an isothermal-isobaric ensemble.

Monte Carlo simulation of a system consisting of 512 cylindrically symmetric particles interacting with each other via a potential which has an isotropic, density dependent part as well as an anisotropic part has been used to simulate the nematic state. The usual Metropolis algorithm is used and the particles are allowed to have translational degrees of freedom along with the orientational one. The simulation has been carried out in an isothermal-isobaric (NPT) ensemble and the multiple histogram technique of Ferrenberg-Swendsen with appropriate modification for the NPT ensemble has been used.

Monte Carlo simulation of a planar lattice model with P4 interactions.

Monte Carlo study of a two-dimensional lattice with three-dimensional spins (d=2,n=3) interacting with nearest neighbors via a -P4(cos theta) potential, where P4 is the fourth Legendre polynomial and theta is the angle between two spins, has been reported for lattice sizes ranging from 10 x 10 to 160 x 160. A cluster algorithm for spin updating with a histogram reweighting technique has been used and finite size scaling has been performed. The model exhibits a strong first order phase transition at a dimensionless temperature 0.