Theory and simulation of biaxial nematic and orthogonal smectic phases formed by mixtures of board-like molecules

Variational cluster calculations and Monte Carlo simulations are applied to hard-body board-like models of biaxial molecules forming liquid crystalline phases. The molecular long axes are assumed for simplicity to be fully oriented. Depending on the extent of transverse anisometry in the molecular shape, these systems can exhibit biaxial nematic phases as well as uniaxial and biaxial orthogonal smectic phases. It is shown that the region of thermodynamic stability for the biaxial nematic phase is considerably broadened in binary mixtures of molecules with the same cross section but differing in their long dimension.