Columnar phases of discotic spherocylinders.

The liquid crystal phase diagram of the discotic hard spherocylinder fluid is investigated by Monte Carlo simulations. Thickness-to-diameter aspect ratios within L/D=0.2-0.5 are considered. Three distinct columnar phases are found, namely, a hexatic interdigitated phase (D(hi)), a hexatic ordered phase (D(ho)), both with long-range spatial correlations, and a hexatic disordered phase (D(hd)), in which the columns become fluidlike. Local domains of stacked particles are also observed in the isotropic phase. The stability of the D(ho) and D(hd) phases is favored with increasing anisotropy of the particle shape. As a consequence, the packing fraction versus the aspect ratio representation of the phase diagram features D(ho)-D(hd)-I and D(hi)-D(ho)-I triple points. The study involved the development of an efficient algorithm to compute the shortest distance between two oblate spherocylinder particles. The study provides a general coarse-grain methodology to explore discotic behavior, with fundamental advantages against alternative molecular models.