A recently developed method for generating distributed, localized atomic polarizabilities
from the ab initio molecular charge density is used to assess the importance of the induction
energy in crystal structures of small organic molecules. Two models are first contrasted
based on large cluster representing the crystalline environment: one using the polarizability
model in which induced multipoles are evaluated in response to the electrostatic field due
to atomic multipoles; the other is a complementary procedure in which the same cluster is
represented by atomic point-charges and the molecular charge density is calculated ab initio
in this environment. The comparable results of these two methods show that the
contribution to the lattice energy from the induction term can differ significantly between
polymorphic forms, for a selection of organic crystal structures including carbamazepine
and oxalyl dihydrazide, and 3-azabicyclo[3,3,1]nonane-2,4-dione. The observed charge
density polarization of naphthalene in the crystalline state is also reproduced.
This demonstrates that explicit inclusion of the induction energy, rather than its absorption
into an empirically fitted repulsion-dispersion potential, will improve the relative ordering
of the lattice energies for computed structures, and that it needs to be included in crystal
structure prediction. Hence, the distributed atomic polarizability model was coded into the
lattice-energy minimization program DMACRYS (which was developed as a Fortran90
recoding of DMAREL) to allow the induction energy to be calculated
