Recommendations of the Ad hoc committee on criteria for publication of charge density studies

Sir, The Committee is of the firm opinion that guidelines should not attempt to prescribe how crystallographic research is to be performed. This is strictly the prerogative of the individual investigator. Also, optimal experimental methodology will vary with time, with available facilities, and with the aims of the research. However, a manuscript should provide the requisite information to allow referees and readers to make an informed judgment about the reliability of the reported conclusions. The amount of detail provided for this purpose should be consonant with the significance explicitly or implicitly claimed for the results presented. The following information, much of which is probably desirable in any crystallographic study claiming high accuracy, should normally be regarded as a near minimum requirement in any publication reporting quantitative charge density results. 1. A full description of basic experimental procedures, such as preparation and testing of crystal specimens, temperature control, incident radiation, scan parameters, monitoring, background determination, etc. 2. How systematic errors such as absorption, extinction, scan truncation and the like were corrected, or why such effects were considered unimportant. 3. The method used for estimating the variances of the measured structure amplitudes. 4. Internal consistency indices if symmetry-equivalent reflections were measured. 5. Evidence for the compatibility of Xray and neutron data if both were used together, particularly with regard to crystal quality and temperature. 6. The method for scaling X-ray data in the calculation of X-X or X-N maps. 7. Complete listing of (anisotropic) atomic vibration parameters, at least for non-hydrogen atoms. 8. Representative residual density maps, or summary descriptions thereof, after the highest level of refinement reported, the required number of such maps depending on the complexity of the structure.