Packing energy, lattice

The assumptions concerning the symmetry of the unit cell noted above have been the basis of recent refinements of the structure of cellulose I. In one such refinement (17) the forbidden reflections were simply assimed negligible, and the intensity data from Valonia cellulose were used to arrive at a final structure. In another study, the inadequate informational content of the diffractometric data was complemented with analyses of lattice packing energies (29) the final structures were constrained to minimize the packing energy as well as optimizing the fit to the diffractometric data. 

The packing energy of an organic crystal can be easily calculated by a lattice sum over pairwise interactions. The potential parameters for these calculations are summarized in Table 15. The packing energy is usually a quite accurate estimate of the crystal sublimation energy. 

FIGURE 21. Packing energy, PE (kcal mol l at 10 A cutoff in the lattice sums), as a function of total molecular free surface, SM, in compounds 1-8. 

Fig. 6a-d. Histograms of differences in properties between polymorphs a AE (packing energy, %) b AD (density, %) c AS (lattice-vibrational entropy, J mol ) d AZ (no. of molecules in the asymmetric unit). (Reprinted with permission from [79], copyright 1995, American Chemical Society)... 

This polymer has been the archetypal one for applications of molecular mechanics to lattice packing. It is found for well-calibrated energy function parameter sets, i.e., force fields , that the crystal structure is rqjroduced well. Table 1 shows a comparison for lattice parameters between a calculation [6] and experiment... 

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