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

Area of Science:

• Computational physics
• Materials science
• Chemical physics

Background:

• First-order phase transitions, like the nematic-isotropic (NI) transition, present sampling challenges in molecular dynamics simulations due to unstable regions.
• Traditional methods such as temperature replica-exchange (tREM) struggle with the potential energy gap between distinct phases.

Purpose of the Study:

• To simulate the NI phase transition of 4-cyano-4'-pentylbiphenyl using an advanced molecular dynamics technique.
• To evaluate the efficacy of the generalized replica-exchange method (gREM) for enhanced configuration sampling.
• To compare the performance of gREM with tREM for first-order phase transitions.

Main Methods:

• Molecular dynamics simulations employing the generalized replica-exchange method (gREM).
• Introduction of an effective temperature in gREM to improve sampling in unstable regions.
• Analysis of sampling performance across various system sizes and comparison with temperature replica-exchange (tREM).

Main Results:

• gREM achieved sufficient replica-exchange acceptance ratios around the NI transition temperature.
• A bimodal distribution of the order parameter was observed at the transition region, consistent with mean-field theory.
• tREM demonstrated ineffectiveness near the transition temperature due to the significant potential energy gap.

Conclusions:

• gREM is a highly effective method for simulating first-order phase transitions, particularly the NI transition.
• The enhanced sampling capability of gREM overcomes limitations faced by tREM in systems with large potential energy barriers.
• Simulation results support theoretical predictions, such as mean-field theory, for phase transition behavior.