Atomistic analysis of nematic phase transition in 4-cyano-4′-n-alkyl biphenyl liquid crystals: Sampling for the first-order phase transition and the free-energy decomposition.

This article focuses on molecular dynamics (MD) simulations of the nematic–isotropic (NI) phase transition in 4-cyano-4′-n-alkyl biphenyl (nCB) liquid crystals with alkyl chain lengths n = 5, 6, 7, and 8, using the generalized replica exchange method (gREM) combined with free-energy calculations based on energy representation (ER) theory. The study demonstrates that gREM effectively samples thermodynamically unstable states near the first-order NI phase transition, while ER theory enables decomposition of the insertion free energy into energetic and entropic contributions, revealing their competing roles in driving the phase transition. The orientational order parameters and distributions obtained from MD simulations show good agreement with the mean-field Maier–Saupe (MS) model, and local orientational correlations indicate short-range antiparallel molecular arrangements in both phases. Additionally, the work identifies an odd–even effect in the alkyl chain length influencing the NI transition temperature and thermodynamic stability, attributed to differences in molecular anisotropy.