  We use the ``isoconfigurational ensemble'' [Phys. Rev. Lett. {\bf 93}, 135701
(2004)] to analyze both dynamical and structural properties in simulations of a
glass forming molecular liquid. We show that spatially correlated clusters of
low potential energy molecules are observable on the time scale of structural
relaxation, despite the absence of spatial correlations of potential energy in
the instantaneous structure of the system. We find that these structural
heterogeneities correlate with dynamical heterogeneities in the form of
clusters of low molecular mobility.
