System-Size Effects on the Molecular Dynamics Simulation of an All-Aromatic Liquid Crystal

Atomistic molecular dynamics simulations are presented for a prototypical all-aromatic calamitic liquid crystal that has recently emerged as a benchmark system for testing theories of nematic order. By performing simulations with progressively larger systems, up to an unprecedented total of 12,600 molecules, we investigate the impact of system size on the structural and dynamic properties of the material in the nematic and smectic A mesophases. Our results demonstrate that using a number of molecules on the order of 104 not only improves statistical sampling, thereby reducing uncertainty in all the computed quantities, but is also necessary to minimize finite-size and boundary-condition effects. This, in turn, enables unbiased estimates of key thermodynamic properties (such as transition temperatures and enthalpies, order parameters, and diffusion coefficients) and allows for a correct determination of the nature of the phase transitions (first- versus second-order). Moreover, we emphasize that large simulation boxes are essential to capture mesoscale structural features with characteristic length scales of several tens of nanometres, underscoring the unique capability of atomistic molecular dynamics simulations to complement experimental studies.