A third blind test of crystal structure prediction

Abstract

Following the interest generated by two previous blind tests of crystal structure prediction (CSP1999 and CSP2001), a third such collaborative project (CSP2004) was hosted by the Cambridge Crystallographic Data Centre. A range of methodologies used in searching for and ranking the likelihood of predicted crystal structures is represented amongst the 18 participating research groups, although most are based on the global minimization of the lattice energy. Initially the participants were given molecular diagrams of three molecules and asked to submit three predictions for the most likely crystal structure of each. Unlike earlier blind tests, no restriction was placed on the possible space group of the target crystal structures. Furthermore, Z' = 2 structures were allowed. Part-way through the test, a partial structure report was discovered for one of the molecules, which could no longer be considered a blind test. Hence, a second molecule from the same category (small, rigid with common atom types) was offered to the participants as a replacement. Success rates within the three submitted predictions were lower than in the previous tests - there was only one successful prediction for any of the three ;blind' molecules. For the ;simplest' rigid molecule, this lack of success is partly due to the observed structure crystallizing with two molecules in the asymmetric unit. As in the 2001 blind test, there was no success in predicting the structure of the flexible molecule. The results highlight the necessity for better energy models, capable of simultaneously describing conformational and packing energies with high accuracy. There is also a need for improvements in search procedures for crystals with more than one independent molecule, as well as for molecules with conformational flexibility. These are necessary requirements for the prediction of possible thermodynamically favoured polymorphs. Which of these are actually realised is also influenced by as yet insufficiently understood processes of nucleation and crystal growth.

Application of computational methods to the design and characterisation of porous molecular materials

“…However, it was found early in the development and evaluation of CSP methods that the transferable force fields with simple forms for atom-atom interactions do not result in reliable, successful predictions. 38 Therefore, CSP has led to the development of more elaborate force field methods 39 and, in recent years, the availability of large scale parallel computing has enabled solid state DFT methods to be applied to CSP, with considerable success. 40 Two of the key current challenges in CSP relate to applications to large and flexible molecules and further improvements to energy models to increase the reliability of predictions.…”

Crystal structure prediction could have helped the experimentalists with polymorphism in benzamide

“…Crystal structure prediction (CSP) represents a fast and cheap method to acquire a general idea of local energy minima on the lattice energy hyper surface. Several different techniques can be found in the literature and the success of these methods is checked regularly [6,7,8]. Rigid body calculations allow a very accurate description of the intermolecular potentials using distributed multipole analysis [9,10,11].…”

Third structure determination by powder diffractometry round robin (SDPDRR-3)

“…A probably nonexhaustive list of published dedicated SDPD software from which structure solution could be expected for one or both samples is as follow ͑alphabetical order͒: DASH . A list of computer programs for the prediction of the packing of molecular structure, which could have been used for the structure solution of sample 1, can be found in Day et al, 2005. The powder patterns for the two samples were experimental, supplied in various standard formats ͑Figures 2-4͒.…”