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Electron density

The electron density of a chemical system is probably the most information-rich observable available to chemistry. A topological analysis of the electron density based on the Quantum Theory of Atoms In Molecules[1] provides invaluable chemical information about the bonding interactions and electronic properties. The electron density has the great advantage that it can be obtained either from quantum mechanical calculations as well as experimentally from accurate X-ray diffraction data. This permits a comparison of theoretical and experimental results on an equal footing.

Static model deformation electron density, ?multipole model(r)-?independent atom model(r), in two planes for the pyrite polymorph of FeS2 obtained from single crystal X-ray diffraction.[2] Positive and negative contours are shown with blue and red lines, respectively. Charge accumulation is clearly seen in the S-S bond, showing the covalency of the bond. On iron charge is redistributed in agreement with the crystal field splitting, but some charge is accumulated midway along the Fe-S bond, indicating some degree of covalency. Results published in Chemical Science, doi: 10.1039/C3SC52977K
Charge concentrations derived from a theoretical B3LYP/6-311G** electron density obtained for the experimentally determined geometry of a one-coordinate Ga(I) amide.[3] The tetrahedral arrangement of the nitrogen charge concentrations indicate that nitrogen is sp3 hybridized with two sigma-bonds to carbon and silicon and two lone pairs pointing towards gallium in a scissor grasp. Charge concentrations are depicted as red balls. Hydrogen atoms are omitted for clarity.
Molecular graph of rubrene endoperoxide derived from a theoretical B3LYP/6-311++G(d,p) electron density in the experimentally determined geometry.[4] Bond critical points are depicted as orange dots. Hydrogen atoms are omitted for clarity.

[1] Bader, R. F. W. Atoms in molecules : a quantum theory; Clarendon Press: Oxford, 1990.

[2] Schmokel, M. S.; Bjerg, L.; Cenedese, S.; Jorgensen, M. R. V.; Chen, Y. S.; Overgaard, J.; Iversen, B. B. Chem Sci 2014, 5, 1408.

[3] Thomsen, M. K.; Dange, D.; Jones, C.; Overgaard, J. Chem-Eur J 2015, 21, 14460.

[4] doi: 10.1021/acs.jpca.6b06588