  Modeling the dielectric behavior of molecular materials made up of large
pi-conjugated molecules is an interesting and complex task. Here we address
linear polarizabilities, and the related dielectric constant, of molecular
crystals and aggregates made up of closed-shell pi-conjugated molecules with
either a non-polar or largely polar ground-state, and also examine the behavior
of mixed-valence (or charge-transfer) organic salts. We recognize important
collective phenomena due to supramolecular interactions in materials with large
molecular polarizabilities, and underline large vibrational contributions to
the polarizability in materials with largely delocalized electrons.
