plane of the terminal CH 2
• group, where the very large spin density value is
essentially determined by the carbon carrying the unpaired electron and where the
role of its linked hydrogen and carbon atoms is just that of neutralize the slight αeffect excess arising from the radicalic carbon.
In general, joint analyses of the spin and electron density source functions
provide interesting insights, as the different way the two scalar fields dilute and
concentrate in the space lead to reconstructions of these fields which may be totally
different. For example, this is the case of the points associated to the lone pair
electrons in water triplet [94] or the just mentioned case of the spin density at the
terminal C–H bcp in n-alkyl radicals.
Being defined in term of observables, the Source Function tool is amenable to
experimental determination. This is already a standard practice for the electron
density. The latter has become almost routinely accessible, even from microcrystals,
due to the impressive advance of the photon source technology and the developments of modern multipole methods (including the availability of pole libraries) [9].
The electron spin density is, however, also becoming more and more within reach,
experimentally [96]. The ongoing possibility of an unbiased comparison of ab initio
and experimental (polarized neutrons plus X-rays) spin densities is of a paramount
importance for the molecular-scale design of novel magnetic materials. Electron
spin densities are known to be very sensitive to the adopted theoretical framework
[94], while several technical limitations arise when experimental results are considered [9]. The Source Function could be a valuable tool in such regard. It shows
how the electron spin density is determined in the various molecular regions and,
therefore, it could also neatly disclose the cause behind an observed, significant spin
density difference or behind a particular spin density sensitivity to computational
and methodological parameters.
Acknowledgments We thank the Danish National Research Foundation for partial funding of
this work through the Center for Materials Crystallography (DNRF93).
References
1. Bader RFW, Gatti C (1998) A Green’s function for the density. Chem Phys Lett 287:233–238
2. Gatti C (2012) The source function descriptor as a tool to extract chemical information from
theoretical and experimental electron densities. Struct Bond 147:193–286
3. Gatti C (2013) Challenging chemical concepts through charge density of molecules and
crystals. Phys Scripta 87:048102 (38 pp)
4. Arfken G (1985) Mathematical methods for physicists. Academic Press, Orlando
5. Bader RFW (1990) Atoms in molecules: a quantum theory. In: International series of
monographs on chemistry, vol 22. Oxford Science Publications, Oxford UK
6. Gatti C, Cargnoni F, Bertini L (2003) Chemical information from the source function.
J Comput Chem 24:422–436
7. Hansen NK, Coppens P (1978) Electron population analysis of accurate diffraction data. 6.
testing aspherical atom refinements on small-molecule data sets. Acta Cryst A 34:909–921
5 Exploring Chemistry Through the Source Function …
125
• group, where the very large spin density value is
essentially determined by the carbon carrying the unpaired electron and where the
role of its linked hydrogen and carbon atoms is just that of neutralize the slight αeffect excess arising from the radicalic carbon.
In general, joint analyses of the spin and electron density source functions
provide interesting insights, as the different way the two scalar fields dilute and
concentrate in the space lead to reconstructions of these fields which may be totally
different. For example, this is the case of the points associated to the lone pair
electrons in water triplet [94] or the just mentioned case of the spin density at the
terminal C–H bcp in n-alkyl radicals.
Being defined in term of observables, the Source Function tool is amenable to
experimental determination. This is already a standard practice for the electron
density. The latter has become almost routinely accessible, even from microcrystals,
due to the impressive advance of the photon source technology and the developments of modern multipole methods (including the availability of pole libraries) [9].
The electron spin density is, however, also becoming more and more within reach,
experimentally [96]. The ongoing possibility of an unbiased comparison of ab initio
and experimental (polarized neutrons plus X-rays) spin densities is of a paramount
importance for the molecular-scale design of novel magnetic materials. Electron
spin densities are known to be very sensitive to the adopted theoretical framework
[94], while several technical limitations arise when experimental results are considered [9]. The Source Function could be a valuable tool in such regard. It shows
how the electron spin density is determined in the various molecular regions and,
therefore, it could also neatly disclose the cause behind an observed, significant spin
density difference or behind a particular spin density sensitivity to computational
and methodological parameters.
Acknowledgments We thank the Danish National Research Foundation for partial funding of
this work through the Center for Materials Crystallography (DNRF93).
References
1. Bader RFW, Gatti C (1998) A Green’s function for the density. Chem Phys Lett 287:233–238
2. Gatti C (2012) The source function descriptor as a tool to extract chemical information from
theoretical and experimental electron densities. Struct Bond 147:193–286
3. Gatti C (2013) Challenging chemical concepts through charge density of molecules and
crystals. Phys Scripta 87:048102 (38 pp)
4. Arfken G (1985) Mathematical methods for physicists. Academic Press, Orlando
5. Bader RFW (1990) Atoms in molecules: a quantum theory. In: International series of
monographs on chemistry, vol 22. Oxford Science Publications, Oxford UK
6. Gatti C, Cargnoni F, Bertini L (2003) Chemical information from the source function.
J Comput Chem 24:422–436
7. Hansen NK, Coppens P (1978) Electron population analysis of accurate diffraction data. 6.
testing aspherical atom refinements on small-molecule data sets. Acta Cryst A 34:909–921
5 Exploring Chemistry Through the Source Function …
125