Elastic properties of common Gay–Berne nematogens from density of states (DOS) simulations

ABSTRACT

A free energy perturbation method is used to systematically study the elastic properties of four common Gay–Berne nematogenic models; two with a length-to-diameter ratio κ = 3 [(3, 5, 1, 2) and (3, 5, 1, 3)], a model with κ = 4.4 parameterised for p-terphenyl (4.4, 20, 1, 1), and a discogen with κ = 0.345 (0.345, 0.2, 1, 2). In accordance with previous measurements, we find that for κ = 3, models, . We additionally find the latter two models in particular accurately capture the experimentally measured elastic ratios in apolar achiral systems. The (4.4, 20, 1, 1) model reproduces the elastic constant ratios of p-azoxyanisole remarkably well, and maps to within 30% of the absolute. The (0.345, 0.2, 1, 2) model elastic constants exhibit an unusual temperature dependence similar to recent experimental studies. Here we find , in line with theoretical predictions. All models deviate from the mean-field expectation k_ii ∝ S². These results represent a crucial first step towards quantitatively accurate coarse-grained liquid crystalline models of self-assembly and response, enabling one to choose a Gay–Berne model based on its measured elastic ratios rather than just its shape and energy anisotropy.

Graphical Abstract

KEYWORDS:

• Elastic constants
• Monte Carlo
• free energy
• Gay–Berne model
• density of states

Acknowledgements

HS and JKW acknowledge computational resources at the Notre Dame Center for Research Computing (CRC). This work was supported by MICCoM, as part of the Computational Materials Sciences Program funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under grant #0J-30521-0009A.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by MICCoM, as part of the Computational Materials Sciences Program funded by the Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division [Grant Number 0J-30521-0009A].