Recently we have applied techniques that use density building functions and density histogram matching methods coupled with entropy maximisation and likelihood analysis to solve a number of structures ab initio using electron diffraction data in 2- and 3-dimensions at resolutions that are often around 2A. [1]. The same methodology can be used very effectively with powder diffraction data:

1. A low resolution structure is generated using non-overlapped low resolution structure factors combined with the origin defining rules of direct methods.
2. New reflections are given permuted phase angles (and intensities if overlapped) and analysed using density building functions [2].
3. The optimal phase sets are subjected to entropy maximisation [3].
4. Likelihood and density histogram matching are used to select the optimal phase set.

The method is very simple to use, works automatically and is very effective at low resolution (ca. 2A) where traditional reciprocal methods can struggle. Inn these cases it gives excellent molecular envelopes that can be used by the FOCUS software [4].

Applications to a number of varied zeolite systems will be presented including EMM-3, EMM-8, ECR-40, DOH, MCM-70 and some unsolved structures. A typical envelope for DOH [5] is shown below.

Figure: Envelope for DOH using laboratory data.

The use successful of charge flipping algorithms [6] with some of this data will also be discussed.

[1] Dorset, D.L., Dong, W. & Gilmore, C.J. Acta Cryst. (2008). A64, 284-294; 295-302.

[2] Gilmore, C.J., Bricogne, G & Bannister, C. (1990). Acta Cryst. A46, 297-308.

[3] Bricogne, G & Gilmore, C.J. (1990). Acta Cryst. A46, 284-297.

[4] Grosse-Kunstleve, R.W., McCusker, L.B. & Baerlocher, Ch. (1999). J. Appl. Cryst. 32, 536-542.

[5] Gerke, H. & Gies, H (1984) 166, 11-22.

[6] Oszlanyi, G & Suto, A (2004). Acta Cryst A60, 134-141.

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