CLRC NEWS
In the last issue I reported the Council for the Central Laboratory of the Research Councils was established by Royal Charter on 1 April 1995, with the abbreviation CCL The previous name DRAL is no longer in use for DL + RAL.The abbreviation 'CCL' has given rise to difficulties and ambiguities where other organisation are already using CCL as their title; the four letters 'CLRC' may be used as an abbreviation for the Central Laboratory of the Research Councils. It operates from three sites, the Chilbolton Observatory in Hampshire, the Daresbury Laboratory (DL) in Cheshire and Rutherford Appleton Laboratory, (RAL) in Chilton. The official logo is shown above, I think the official name for the diagram is 'the swirl', but I have yet to understand its significance.
So the CLRC news for this issue is a report by Ron Smith on the
crystallographic instruments at ISIS, one from Bill David on the successful
IUCr workshop held in Abingdon (read about
William Bragg's nephew), and one from Tony Holland on the setting up of
SDPD95
Structure Determination from Powder Diffraction Data
SDPD95, an IUCr workshop focussing on structure determination from powder diffraction data, was held at Wadham College, Oxford between 16th and 20th July 1995. Powder diffraction is now perhaps best known for the impact that the Rietveld method has made in the refinement of structures and, in particular, the structures of the high temperature superconductors. Over the past five years, however, as a result of improvements in diffraction instrumentation and computer hardware and software, there have been major advances in ab-initio structure determination from powder data. Judging by the 200+ requests for registration, the field is already well-developed. However, because of the workshop nature of the meeting, attendance was limited to 100 participants (from 27 countries) with 20 lecturers.After an evening reception in the University Museum, the meeting began in earnest on Monday with a day of introductory lectures at the Rutherford Appleton Laboratory. Tony Cheetham (Santa Barbara) gave an impressive display of solved structures some with excess of 50 atoms in the asymmetric unit. In conclusion, he observed that in future, the problem may not be the solution of structures but their accurate refinement from powder data. Daniel Louer (Rennes), Dave Cox (Brookhaven) and Bill David (ISIS) respectively pointed out the advances in laboratory X-ray, synchrotron X-ray and neutron powder diffraction analysis and instrumentation. This was followed by Andy Fitch (ESRF) who showed that combining X-ray and neutron techniques was often the most desirable approach. With only a tour of the ISIS spallation neutron as light relief (!), the working day finished with two talks by John Newsam and Clive Freeman (BIOSYM) who demonstrated the powerful visualisation and simulation tools available for powder diffraction studies.
After an exhausting seven hours of talks, the conference decamped to Lains Barn, a converted 300-year old barn, for an evening of good food and wine in magnificent surroundings courtesy of Dick Squires, a retired country doctor who had restored the barn. And here I must tell you a little story. As the meal was finishing, Dick came up to me and said, 'Shall I say a little about the barn?' to which I said 'Yes' and then he followed with 'I believe you are a group of crystallographers'. As most crystallographers are aware, this usually marks the end of the conversation, either that or the conversation moves tangentially on to the mystical powers of crystals. So I politely answered in the affirmative. This was followed not by silence but by the follow-up 'My uncle was quite a famous crystallographer.' Again believing that the end of the conversation was nigh, I enquired, expecting never to have heard of this famous man, only to be told 'My uncle Will', 'William Bragg'. He then added to his history of the barn some delightful anecdotes of William Bragg that rounded off a full and eventful day.
The rest of the meeting was based at Wadham College with the main lectures taking place in the Holywell Music Room. Constructed in 1748, it is probably the oldest public concert hall in Europe which is still in regular use. A poster session with around 30 excellent contributions was in continuous running during the coffee and lunch breaks. Tuesday focussed on the principal steps of structure solution. Rod Hill (CSIRO, Melbourne) highlighted the importance of correct sample preparation and data collection which was followed by an explanation of powder indexing methods by Per-Erik Werner (Stockholm). Devinder Sivia (ISIS) emphasised the advantages of a Bayesian approach for peak finding and structure factor extraction from powder diffraction data. Rene Peschar (Amsterdam) and Carmelo Giacovazzo (Bari) introduced the principles of Direct Methods and their particular application to powder diffraction data. The meeting then divided into four groups led by tutors. This afternoon workshop format that remained the pattern for the rest of the meeting proved to be very popular. Neither the excellent weather nor the nearby attractions of Oxford diminished the numbers at these parallel sessions which varied from small masterclasses, through BIOSYM and Siemens demonstrations to tutorials based around computer demonstrations.The Wednesday morning lectures were devoted to the MaxEnt approach to structure solution developed by Gerard Bricogne (Cambridge & Paris) who gave an introductory lecture on the theoretical aspects of MaxEnt structure solution. This was followed by practical aspects and particular problems given by Chris Gilmore (Glasgow) and Kenneth Shankland (ISIS) respectively. After a full afternoon of tutorials and masterclasses, we were treated to the proper use of the Holywell Music Room by the Frideswide ensemble who, in the evening, returned us to the 18th century with arias and music on period instruments by Purcell, Handel and Ostwald. The final day of the meeting was devoted to an excellent appraisal of Patterson methods by Michael Estermann (Zurich), followed by a description of old and new applications of chemical knowledge to structure solution, particularly in the case of zeolites by Lynne McCusker (Zurich). The final talk by Christian Baerlocher (Zurich) was a typically restrained and refined rendition of 'Restrained refinement'. After an afternoon of tutorials and masterclasses, the meeting ended with a excellent banquet in the magnificent surroundings of Wadham College Hall accompanied by the minimum of speeches.
We judged the meeting to be a success. Structure determination from powder diffraction data has developed significantly over recent years and the meeting provided the first opportunity for a general discussion of the problems as well as the successes. Now that you have heard about the conference, get ready to read the book which we hope will be published in the OUP/IUCr monograph on crystallography series!
Bill David,
ISIS
3 August 1995
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