Monte Carlo simulation of a disclination core in nematic solutions of rodlike molecules

The core structure of a disclination line defect in a nematic liquid crystal is simulated by a Monte Carlo technique in which molecules are represented as hard spherocylinders, with aspect ratios ranging from 5 to 15. For small aspect ratios (5 and 8), we confirm the mean-field Landau theory that the core is biaxial with negative order parameter at the center. The order parameter coherence length is small, of the order of the molecular diameter. For large aspect ratios, we discover a new microscopically ``escaped'' structure for -1/2 wedge disclinations, in which the molecules point predominantly along the disclination line. Free energy calculations demonstrate that the ``escaped'' structure is of lower energy than the unescaped ``flat'' structure, which is metastable. We expect the ``escaped'' structure to retard disclination mobility.