  Semiflexible polymers in concentrated lyotropic solution are studied within a
bead-spring model by molecular dynamics simulations, focusing on the emergence
of a smectic A phase and its properties. We systematically vary the density of
the monomeric units for several contour lengths that are taken smaller than the
chain persistence length. The difficulties concerning the equilibration of such
systems and the choice of appropriate ensemble (constant volume versus constant
pressure, where all three linear dimensions of the simulation box can fluctuate
independently) are carefully discussed. Using HOOMD-blue on graphics processing
units, systems containing more than a million monomeric units are accessible,
making it possible to distinguish the order of the phase transitions that
occur. While in this model the nematic-smectic transition is continuous, the
transition from the smectic phase to a related crystalline structure with true
three-dimensional long-range order is clearly of first order. Further, both
orientational and positional correlations of monomeric units are studied as
well as the order parameters characterizing the nematic, smectic A, and
crystalline phases. The analogy between smectic order and one-dimensional
harmonic crystals with respect to the behavior of the structure factor is also
explored. Finally, the results are put in perspective with pertinent
theoretical predictions and possible experiments.
