Recently, a new class of smectic liquid crystal phases characterized by the spontaneous formation of macroscopic chiral domains from achiral bent-core molecules has been discovered. We have carried out Monte Carlo simulations of a minimal hard spherocylinder dimer model to investigate the role of excluded volume interactions in determining the phase behavior of bent-core materials and to probe the molecular origins of polar and chiral symmetry breaking. We present the phase diagram of hard spherocylinder dimers of length-diameter ratio of 5 as a function of pressure or density and dimer opening angle $\psi .$ With decreasing $\psi ,$ a transition from a nonpolar to a polar smectic A phase is observed near $\psi =167\mathrm{}°,$ and the nematic phase becomes thermodynamically unstable for $\psi <135\mathrm{}°.$ Free energy calculations indicate that the antipolar smectic A $\left(\mathrm{Sm}A{\mathrm{P}}_A\right)$ phase is more stable than the polar smectic A phase $\left(\mathrm{Sm}A{\mathrm{P}}_F\right).\mathrm{}$ No chiral smectic or biaxial nematic phases were found.

• Received 26 August 2002

DOI:https://doi.org/10.1103/PhysRevE.67.011703