Significant progress in predicting the crystal structures of small organic molecules--a report on the fourth blind test.

We report on the organization and outcome of the fourth blind test of crystal structure prediction, an international collaborative project organized to evaluate the present state in computational methods of predicting the crystal structures of small organic molecules. There were 14 research groups which took part, using a variety of methods to generate and rank the most likely crystal structures for four target systems: three single-component crystal structures and a 1:1 cocrystal. Participants were challenged to predict the crystal structures of the four systems, given only their molecular diagrams, while the recently determined but as-yet unpublished crystal structures were withheld by an independent referee. Three predictions were allowed for each system. The results demonstrate a dramatic improvement in rates of success over previous blind tests; in total, there were 13 successful predictions and, for each of the four targets, at least two groups correctly predicted the observed crystal structure. The successes include one participating group who correctly predicted all four crystal structures as their first ranked choice, albeit at a considerable computational expense. The results reflect important improvements in modelling methods and suggest that, at least for the small and fairly rigid types of molecules included in this blind test, such calculations can be constructively applied to help understand crystallization and polymorphism of organic molecules.

A Distributed Computing Method for Crystal Structure Prediction of Flexible Molecules: An Application to N-(2-Dimethyl-4,5-dinitrophenyl) Acetamide.

In this paper, we describe a new distributed computing framework for crystal structure prediction that is capable of performing crystal structure searches for flexible molecules within any space group and with an arbitrary number of molecules in the asymmetric unit. The distributed computing framework includes a series of tightly integrated computer programs for generating the molecule's force field, sampling possible crystal structures using a distributed parallel genetic algorithm, locally minimizing these structures and classifying, sorting, and archiving the most relevant ones. As an example, we report the results of its application to the prediction of the crystal structure of the elusive N-(2-dimethyl-4,5-dinitrophenyl) acetamide, a molecule for which its crystal structure proved to be one of the most difficult cases in the last CSP2004 blind test for crystal structure prediction.

Theoretical study of the adsorption of H on Si n clusters, (n=3-10).

A recently proposed local Fukui function is used to predict the binding site of atomic hydrogen on silicon clusters. To validate the predictions, an extensive search for the more stable SinH (n=3-10) clusters has been done using a modified genetic algorithm. In all cases, the isomer predicted by the Fukui function is found by the search, but it is not always the most stable one. It is discussed that in the cases where the geometrical structure of the bare silicon cluster suffers a considerable change due to the addition of one hydrogen atom, the situation is more complicated and the relaxation effects should be considered.