Chemistry Reference
In-Depth Information
Computational Studies of Crystal Structure
and Bonding
Angelo Gavezzotti
Abstract The analysis, prediction, and control of crystal structures are frontier
topics in present-day research in view of their importance for materials science,
pharmaceutical sciences, and many other chemical processes. Computational
crystallography is nowadays a branch of the chemical and physicals sciences
dealing with the study of inner structure, intermolecular bonding, and cohesive
energies in crystals. This chapter, mainly focused on organic compounds, first
reviews the current methods for X-ray diffraction data treatment, and the new
tools available both for quantitative statistical analysis of geometries of intermo-
lecular contacts using crystallographic databases and for the comparison of
crystal structures to detect similarities or differences. Quantum chemical methods
for the evaluation of intermolecular energies are then reviewed in detail: atoms-
in-molecules and other density-based methods, ab initio MO theory, perturbation
theory methods, dispersion-supplemented DFT, semiempirical methods and,
finally, entirely empirical atom-atom force fields. The superiority of analyses
based on energy over analyses based on geometry is highlighted, with caveats on
improvised definitions of some intermolecular chemical bonds that are in fact no
more than fluxional approach preferences. A perspective is also given on the
present status of computational methods for the prediction of crystal structures: in
spite of great steps forward, some fundamental obstacles related to the kine-
tic-thermodynamic dilemma persist. Molecular dynamics and Monte Carlo meth-
ods for the simulation of crystal structures and of phase transitions are reviewed.
These methods are still at a very speculative stage, but hold promise for substan-
tial future developments.
Keywords Crystallographic computing
Intermolecular energies
Organic
crystals
