Simulating the nematic-isotropic phase transition of liquid crystal model via generalized replica-exchange method

TL;DR

This paper introduces a generalized replica-exchange method (gREM) for molecular dynamics simulations to effectively sample configurations during the nematic-isotropic phase transition in liquid crystals, overcoming limitations of traditional methods.

Contribution

The paper develops and demonstrates a gREM approach that enhances sampling efficiency in first-order phase transitions, outperforming the traditional tREM method in liquid crystal simulations.

Findings

gREM achieves higher replica-exchange acceptance ratios near transition temperature.

A bimodal distribution of the order parameter confirms the phase transition.

gREM outperforms tREM in sampling configurations around the NI transition.

Abstract

The nematic-isotropic (NI) phase transition of 4-cyano-4'-pentylbiphenyl (5CB) was simulated using the generalized replica-exchange method (gREM) based on molecular dynamics simulations. The effective temperature is introduced in gREM, allowing the enhanced sampling of configurations in the unstable region, which is intrinsic to the first-order phase transition. The sampling performance was analyzed with different system sizes and compared with that of the temperature replica-exchange method (tREM). It was observed that gREM is capable of sampling configurations at sufficient replica-exchange acceptance ratios even around the NI transition temperature. A bimodal distribution of the order parameter at the transition region was found, which is in agreement with the mean-field theory. In contrast, tREM is ineffective around the transition temperature owing to the potential energy gap between the nematic and isotropic phases.