  By employing Molecular Dynamics computer simulations, the phase behavior of
systems of rodlike particles with varying degree of internal flexibility has
been traced from the perfectly rigid rod limit till very flexible particles,
and from the high density region till the isotropic phase. From the perfectly
rigid rod limit and enhancing the internal flexibility, the range of the
smectic A phase is squeezed out by the concomitant action of the scarcely
affected crystalline phase at higher density and the nematic phase at lower
density, until it disappears. These results confirm the supposition, drawn from
previous theoretical, simulational and experimental studies, that the smectic A
phase is destabilized by introducing and enhancing the degree of particle
internal flexibility. However, no significant changes in the order of
nematic--to--smectic A phase transition, which appears always first order, nor
in the value of the layer spacing, are observed upon varying the degree of
particle internal flexibility. Moreover, no evidence of a columnar phase, which
was tought of as a possible superseder of the smectic A phase in flexible rods,
has been obtained.
