ISSN:
1600-5724
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
Charge-density analyses have been carried out on twelve sets of X-ray data. For materials containing first-row atoms intensities measured by the θ:2θ method yield gross populations concordant with electronegativities and the shapes of the distributions agree qualitatively with predictions from force-field arguments. Gross charges are sensitive to experimental errors systematic with Bragg angle, but are insensitive to deficiencies in the models for thermal motion. Noise in thermal parameters is a limiting factor for hydrogen populations determined from X-ray data alone, but mechanistic models for the hydrogen motions obviate this difficulty. Spherically symmetric functions centred at the nuclei give a poor representation of the density for bonded hydrogen. Slater-type orbital products with standard molecular exponents sample the valence density less efficiently for second-row atoms than for carbon, nitrogen and oxygen atoms. Two-centre density functions overlap heavily with neighbouring one-centre terms, and do not provide a useful extension to basis sets for charge-density studies. There are discrepancies between experimental populations and semi-empirical INDO calculations for strongly polar systems.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0567739475000198
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