Crystal structures, predicted

Gavezzotti A 1994. Are Crystal Structures Predictable Accounts of Chemical Research 27 309-314. 

Price SSL, Price LS (2005) Modelling Intermolecular Forces for Organic Crystal Structure Prediction 115 81-123... 

Both thermodynamic and kinetic factors need to be considered. Take, for instance, acetic acid. The liquid contains mostly dimer but the crystal contains the catemer and no (polymorphic) dimer crystal has ever been obtained. Various computations (R. S. Payne, R. J. Roberts, R. C. Rowe, R. Docherty, Generation of crystal structures of acetic acid and its halogenated analogs , J. Comput. Chem, 1998, 19,1-20 W. T. M. Mooij, B. P. van Eijck, S. L. Price, P. Verwer, J. Kroon, Crystal structure predictions for acetic acid , J. Comput. Chem., 1998, 19, 459-474) show the relative stability of the dimer. Perhaps the dimer is not formed in the crystal because it is 0-dimensional and as such, not able to propagate so easily to the bulk crystal as say, the 1-dimensional catemer. 

Ouvrard, C., Price, S.L., 2004, Toward Crystal Structure Prediction for Conformationally Flexible Molecules The Headaches Illustrated by Asprin, Crystal Growth and Design, Vol.4, No. 6, 1119-1127. 

As the above results show, the gross features of the cellulose I crystal structure predicted by various methods do not differ appreciably, but the accompanying deviations in the R -factors are significant. When these predictions are used to assess, for example, whether the cellulose I crystal structure is based on parallel- or antmarallel-chains, the range in the R"-factors seen for the parallel models (cf. Table II) is comparable to that between the two different polarity models. As shown in Fig. 5, the most probable parallel- and antiparallel-chain structures of cellulose I, refined by minimizing the function O, differ in R -factors by approximately the same extent as the three predictions for the parallel model shown in Fig. 4 and Table II. 

Ammon, H. L., Z. Du, and J. R. Holden. 1992. Beyond density prediction to ab initio crystal structure prediction. 11th Annual Working Group Institute on Synthesis of High Energy Density Proceedings. Kiamesha Lake, NY. 15-31. 

Fig. 10 Two molecules proposed as targets for crystal structure prediction in the first blindfold test...

Fig. 11 The giant flexible molecule proposed as one of the six targets in the last crystal structure prediction blindfold test...

There is no doubt that a giant step forward has been made in crystal structure prediction by coupling sound theoretical means with massive computer power, but the inherent uncertainties related to randomness and to handling of temperature remain - see above improvement in force fields and in computational procedures, as results demonstrate, are very welcome but are neither indispensable nor sufficient. And there is no hope that this barrier may fall in the future, as it stems from first principles. The next step forward is the inclusion of kinetic energies and temperature in the model. This is already possible, although with great limitations, as described in Sect. 6. 

Gao, D. and Williams, D. E. (1999). Molecular packing groups and ab initio crystal structure prediction. Acta Cryst. A55, 621-7. 

This kind of crystal design is more often a failure than a success, and crystal structure prediction, particularly hard crystal structure prediction is still extremely difficult (Section 8.8). Generally, a large majority of the currently known host structures discussed in Chapter 7, for example, were discovered by accident rather than design. However, as our knowledge of the factors involved grows, in tandem with more powerful computational and modelling tools, more successes may be expected. 

Table 8.4 Complementary experimental and theoretical techniques in crystal structure prediction.78...

The state of the art in crystal structure calculation is tested every few years in the crystal structure prediction blind tests organised by the Cambridge Crystallographic Data Centre (CCDC). As of the... 

Progress in crystal structure prediction has been significant in recent years with parallel synthon-based and crystal structure calculation based approaches. Calculations are now sometimes able to correctly determine crystal structure in an ab initio fashion but analysis of synthons can give significant qualitative insight. 

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