Splay and polar order in a system of hard pear-like molecules: confrontation of Monte Carlo numerical simulations with density functional theory calculations

Abstract

Recent experimental discoveries of novel nematic types with polar order, including ferroelectric nematic and splay nematic have brought the resurgence of the interest in polar and modulated phases. One of the most important factors that is widely believed to be crucial for the formation of the new phases is the pear-like shape of the mesogenic molecules. Such molecules were treated using second-virial density functional theory in [De Gregorio, P \textit{et al.}, \textit{Soft Matter}, 2016, \textbf{12(23)}, 5188-5198], where the authors showed that the $K_{11}$ splay elastic constant can become negative due to solely entropic reasons leading to long-range splay and polar correlations. To verify whether the predictions are correct, we performed Monte Carlo simulations of the same hard-core molecules used in the DFT study. As our results suggest, no polar or modulated liquid crystalline phases emerge; polar and splay correlations are at most short-range or completely absent. On the other hand, a polar ferroelectric splay crystal was observed.