  A broad variety of liquids conform to density scaling: relaxation times
expressed as a function of the ratio of temperature to density, the latter
raised to a material constant {\gamma}. For atomic liquids interacting only
through simple pair potentials, the exponent {\gamma} is very nearly equal to
n/3, where n is the steepness of the intermolecular potential, while for
molecular liquids having rigid bonds and built using the same interatomic
potential, {\gamma}>n/3. We find that for this class of molecular liquids
{\gamma}=n/{\delta}, where the parameter {\delta} relates the intermolecular
distance to the density along an isomorph (line of approximately constant
dynamics and structure). {\delta} depends only on the molecular structure and
not the interatomic potential.
