Molecular-dynamics simulation of the smectic-$A^{*}$ twist grain-boundary phase

In this paper we present the results of extensive molecular-dynamics simulations of a model of liquid crystals, in which a twist is imposed on the direction of preferred orientation. On quenching the system from a twisted nematic phase to a state point within the smectic-$A$ phase, we observe a structure which corresponds closely to that of the smectic-$A^{*}$ twist grain-boundary phase. We investigate this structure by means of director and structure factor profiles, and also develop a technique for automatically locating screw dislocations. Applying this technique to the configurations from our simulations, we obtain a defect distribution which is in qualitative agreement with theoretical predictions.