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The Winter Meeting of the American Crystallographic Association. Albuquerque, 3–7 April 1972
Author(s) -
Glusker J. P.
Publication year - 1972
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889872010246
Subject(s) - association (psychology) , crystallography , materials science , chemistry , philosophy , epistemology
The Winter meeting of the ACA at the University of New Mexico and the Hilton Inn opened with a symposium on Experimental and Theoretical Studies of the Electron Density in Crystals and Molecules which will be published as Volume 8 of the Transactions of the ACA. The lectures brought together quantum chemists, interested in the a priori calculation of molecular properties, and the growing number of experimentalists who are attempting to determine accurate charge and spin densities by diffraction (X-ray, electron, and neutron) methods. Since the difference in density between the real molecule and a molecule composed of non-interacting atoms is small, great care must be exercised in both theoretical and experimental approaches. The emphasis to date has been on the attempts to obtain agreement between theory and experiment for small molecules. Such attempts have led to an examination of the validity of various approximations in the theory and to the critical evaluation of experimental error. A number of models for the refinement of quantum mechanical parameters from the experimental data were suggested during the symposium. It appears that the purely theoretical approach may provide the most definitive results for organic molecules containing only a few atoms. For larger molecules, however, the experimental approach, when properly calibrated by comparison with theory, will probably provide most new in formation on complex systems. The importance of a comparison between data from neutron diffraction (scattering by nuclei) and from X-ray diffraction (scattering by electrons) in aiding this calibration (D1, B3) °, and the beneficial effects of data collection at temperatures approaching 0°K (D3), were recognized. The proceedings were enlivend by the display 'for the first time in public' of a real picture of the electron density associated with an atom (A2). The photograph was produced by laser illumination of a hologram obtained from an ap-