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IUCr 1995 Report - Commission on Charge, Spin and Momentum Densities

The Commission continued to promote the study of electron-density distributions in both real and momentum space by bringing together physicists, chemists and crystallographers in conferences, workshops and schools, and by initiating and carrying out projects.

With great sorrow, we learned of the passing away of our member J. Almlof in February 1996.

Meetings of the Commission

The Commission met during the Gordon Research Conference on Electron Distribution and Chemical Bonding in Plymouth, New Hampshire, USA, 2-7 July 1995. The topics discussed included the next Sagamore meeting in Saskatchewan, Canada, organized by B. Robertson. It was decided to use the same schedule as the Gordon Conference. It was also planned to have a tutorial workshop in the days before the conference. The conference proceedings would not be published. It was noted with great pleasure that the organizers of the Gordon Conference maintained contact with the Commission and involved its members in the discussion on the organization of the next Gordon Conference. K. Schwarz and C. Lecomte were selected as Chairman and Vice-Chairman.


La Plata.

An International School and Workshop on Charge Density Analysis was held 18-26 May 1995 in La Plata, Argentina. The School was organized by G. Punte on behalf of the IUCr, our Commission and the National University of La Plata. The main topics of the School were as follows: physical principles of accurate structure analysis; X-ray and synchrotron data collection techniques (including advanced methods); crystallization techniques; electron-density modeling with diffraction data; error analysis of experimental results; theoretical methods in charge-density studies; chemical interpretation of electron density in terms of orbital concepts and topological analysis; calculation of properties from the multipole model; comparison of experimental and ab initio electron densities; application to structural activity problems. The lecturers were P. Coppens (USA), R. Goddard (Germany), P. Mallinson (UK), C. Lehmann (UK), V. Tsirelson (Russia), R. Boese (Germany), J. F. Piniella (Spain). The School was attended by (mainly young) participants from Argentina, USA, UK, France, Germany, Mexico, Chile, Cuba and Uruguay. A few tutorial sessions devoted to the use of the multipole model, theoretical models and error analysis took place. Much attention was paid to the new program package XD (Koritsansky's project of our Commission), where much progress was noted since the Brest meeting.

Gordon Conference.

The Gordon Research Conference on Electron Distribution and Chemical Bonding took place at Plymouth, New Hampshire, USA, 2-7 July 1995. About 75 crystallographers and theoretical chemists discussed experimental determinations, quantum-chemical calculations, and interpretation and use of electron-density distributions. The use of the maximum-entropy method and the contribution of electron diffraction raised much interest and heated discussions.

Second International Workshop on Compton Scattering and Fermiology

The meeting was organized by N. Shiotani in Tokyo, Japan, 28-31 August 1995. 64 scientists from 12 countries attended the meeting with 44 invited talks. Synchrotron radiation has made it possible to use ultra-high momentum resolution (0.02 a.u.) and photon energies up to the electron rest energy can be employed. One of the objects of the fermiology project is to standardize procedures with Si as test case. The results of the various groups show significant differences, probably due to background contribution and multiple scattering. On the theoretical side, quite different methodologies - FLAPW and KKR - yield very similar results. Compton studies on different systems were extensively discussed. Other techniques such as positron annihilation, angle-resolved photoemission and electron Compton scattering contributed to obtain a robust picture of the underlying electronic structure. The next meeting will be hosted by Martin Blume in Brookhaven, USA, in Spring 1998.

Sagamore meeting

The next Sagamore meeting will be organized by B. Robertson in Saskatchewan, Canada, 27 July- 1 August 1997.


1. Fermiology of High-Tc Superconductors via High-Resolution Synchrotron-based Compton Scattering. Owing to the recent arrival of new synchrotron sources and the alertness and initiative of our scientists, the project on fermiology and Compton scattering is thriving, as witnessed by the workshop in Tokyo. Active management by A. Bansil contributes to its success.

2. Density Matrix Project. Since progress seems to run in phase with the Sagamore meetings, new results are expected at the coming conference.

3. Multipole Refinement and Related Topics. A Chairman, C. Lecomte, has been appointed and a concept programme has been devised to make a concerted effort of assessing the various multipole programs in existence and in particular the new program XD that has been developed by T. Koritsanzky et al. under the auspices of the IUCr. The activities of the project will be carried out in close cooperation with those undertaken in the field of the Maximum Entropy Project.

4. Maximum Entropy Project. This topic has led to vigorous scientific discussions during the various conferences organized by the Commission. Recent results obtained by different groups show significant differences. The Chairman of the project, M. Sakata, has formulated the objects of the project and its operating procedures.

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Updated 14th February 1997

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