Solid-state computational models

Discuss how solid-state computational modeling techniques could be used to calculate crystal lattice energies and sublimation energies. 

Theoretical Aspects and Computer Modelling of the Molecular Solid State A. Gavezotti, Ed., John Wiley Sons, New York (1997). 

The generation of carbocations in strongly acidic media, and the characterization of their structure by NMR in the 1950s was a breathtaking accomplishment that led to the award of the Nobel Prize in Chemistry to George Olah. Over the past 50 years NMR spectroscopy has evolved as the most important experimental method for the direct study of structure and dynamics of carbocations in solution and in the solid state. Hans-Ullrich Siehl provides an excellent review of computational studies to model experimental NMR spectra for carbocations. This chapter provides an example of how the fruitful interplay between theory and experiment has led to a better understanding of an important class of reactive intermediates. 

For the solubility of TPA in prepolymer, no data are available and the polymer-solvent interaction parameter X of the Flory-Huggins relationship is not accurately known. No experimental data are available for the vapour pressures of dimer or trimer. The published values for the diffusion coefficient of EG in solid and molten PET vary by orders of magnitude. For the diffusion of water, acetaldehyde and DEG in polymer, no reliable data are available. It is not even agreed upon if the mutual diffusion coefficients depend on the polymer molecular weight or on the melt viscosity, and if they are linear or exponential functions of temperature. Molecular modelling, accompanied by the rapid growth of computer performance, will hopefully help to solve this problem in the near future. The mass-transfer mechanisms for by-products in solid PET are not established, and the dependency of the solid-state polycondensation rate on crystallinity is still a matter of assumptions. 

Structural information at the molecular level can be extracted using a number of experimental techniques which include, but are not restricted to, optical rotation, infra-red and ultra-violet spectroscopy, nuclear magnetic resonance in the solid state and in solution, diffraction using electrons, neutrons or x-rays. Not all of them, however, are capable of yielding structural details to the same desirable extent. By far, experience shows that x-ray fiber diffraction (2), in conjunction with computer model building, is the most powerful tool which enables to establish the spatial arrangement of atoms in polymer molecules. 

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