Unconventional reciprocal and direct space strategies

No matter how advanced, every numerical data processing technique has intrinsic limitations, especially when the complexity of the data increases or when the required information is partially missing, as for example in single crystal diffraction from macromolecules and proteins or in powder 

Therefore, novel techniques potentially applicable to solving crystal structures are under continuous testing and development. A recent collective monograph on the structure determination from powder diffraction data provides an excellent discussion of the problem and introduces different approaches that may be used in its solution. In this chapter, unconventional structure solution methods are only briefly reviewed most of them are still controversial and do not always work well with different kinds of compounds and data, although solutions of several complex structures have been demonstrated. Summarized below are the genetic algorithm, maximum entropy, maximum likelihood, and simulated annealing methods. 

Maximum entropy method is a powerful numerical technique, which is based on Bayesian estimation theory and is often applied to derive the most 

Structure determination from powder diffraction data. lUCr monographs on crystallography 13. W. 1. F. David, K. Shankland, L.B. McCusker, and Ch. Baerlocher, Eds., Oxford University Press, Oxford, New York (2002). 

Harris, R.L. Johnston and B.M. Kariuki, The genetie algorithm Foundations and applications in structure solution from powder diffraction data, Acta Cryst. A54, 632 (1998) K. Shankland, B. David, and T. Csoka, Crystal structure determination from powder difffaetion data by the applieation of a genetie algorithm, Z. Kristallogr. 212, 550 (1997). 

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