Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Chemistry and Pharmacology
If electron density distributions of different provenance need to be compared, the evaluation of the charge contents of peaks in deformation densities is useful (besides the usual comparison of density sections). Since deformation peaks are often of approximately ellipsoidal shape, a procedure is proposed in which a rotation ellipsoid is placed in the peak position so that it encloses the peak and separates it from the neighbouring peaks. The charge contents of the peaks are calculated by numerical integration where positive; zero and negative values of the electron density are treated separately. This can be achieved by a minor alteration of a standard Fourier program. Numerical results are presented for p-dicyanobenzene. The C-C bond peaks contain 0.19-0.26 electrons, and the C-N bond peak about 0.26 electrons.
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