  We present a numerical study of the asymmetric dumbbell model consisting of
``molecules'' constructed as two different-sized Lennard-Jones spheres
connected by a rigid bond. In terms of the largest (A) particle radius, we
report data for the structure and dynamics of the liquid phase for the bond
lengths 0.05, 0.1, 0.2, and 0.5, and analogous data for the plastic-crystal
phase for the bond lengths 0.05, 0.1, 0.2, and 0.3. Structure is probed by
means of the AA, AB, and BB radial distribution functions. Dynamics is probed
via the A and B particle mean-square displacement as functions of time and via
the rotational time-autocorrelation function. Consistent with the systems'
strong virial potential-energy correlations, the structure and dynamics are
found to be isomorph invariant to a good approximation in reduced units, while
they generally vary considerably along isotherms of the same (20%) density
variation. Even the rotational time-autocorrelation function, which due to the
constant bond length is not predicted to be isomorph invariant, varies more
along isotherms than along isomorphs. Our findings provide the first validation
of isomorph-theory predictions for plastic crystals for which isomorph
invariance, in fact, is found to apply better than in the liquid phase of
asymmetric-dumbbell models.
