Welch, G.W.A.; (2010) The induction contribution to the lattice energy of organic crystals. Doctoral thesis , UCL (University College London).

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Abstract

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.

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