Long-range decay of pair correlations and nematic ordering in a two-dimensional system of Gay-Berne mesogens

Isothermal-isobaric(NPT) Monte-Carlo simulation has been used to investigate the nature of pair-correlations and ordering in a two-Dimensional system of soft ellipses with aspect ratio κ=3 interacting via the Gay-Berne potential. The system is found to exhibit an isotropic phase (with exponential decay of orientational correlations) and a nematic phase (with algebraic decay of orientational correlations) as we suitably change temperature and pressure. The large distance decay exponent of the orientational correlations is found to converge around an universal value of 0.5 with the increase in pressure along an isotherm. The algebraic decay of orientational correlation in the low temperature phase shows that the nematic lacks true-long range orientational order. This has been substantiated by the system size dependence of the nematic order parameter. We have found the emergence of localized nematic patches separated by disclinations on increasing the pressure in the isotropic phase. No abrupt change is observed in pressure-density plot corresponding to the isotherms studied in this work.