Coarse-Grained Molecular Dynamics Simulations of the Phase Behavior of the 4-Cyano-4′-pentylbiphenyl Liquid Crystal System

Abstract

In this paper, with the aim to establish a rational coarse-grained (CG) model for the 4-cyano-4'-pentylbiphenyl (5CB) molecule, we construct three possible CG models (5P, 6P, and 7P) and then determine the bonded and nonbonded interaction parameters separately. For the intramolecular bonded interactions, the bond and angle distributions of the 5CB bulk phase are used as the target properties. For the nonbonded interactions between CG particles, we combine the structure-based and thermodynamic quantities-based methods for the parametrization of CG interaction potentials and attempt to use several fragment molecular systems to derive the CG nonbonded interaction parameters in order to maintain the transferability of our CG models to some extent. Finally, we fix the optimal nonbonded LJ parameters between CG bead pairs such that the results from CG simulations not only correctly reproduce the experimental density and the nematic LC state at 300 K and 1 atm but also reasonably approximate the local structural properties calculated from the underlying atomistic model. Through comparison of the resulting CG data with target properties, the 6P model is found to be the best one among the three, and then we use this model to investigate the phase behavior and dynamic properties. Our results show that the phase transition temperature from nematic to isotropic phase and the diffusion coefficients are reproduced very well, demonstrating the rationality of the 6P model. Our coarse-grained process should have implications for constructing CG models for nCB series or molecules with similar architectures.