The origins of electronic distortion

The asymmetry found in the electron density of these soft ions can be modelled by adding one or more point multipoles to the point charge used to 

Before one can calculate the bond flux directly, both the magnitude and the orientation of the multipole must be determined, and these are generally not 

The theoretical bond valence, which is calculated using the equal valence rule (3.4), clearly gives a very poor estimate of both the flux and the experimental bond valence since in these compounds the valence is not equally distributed between the bonds. Nevertheless, it provides a useful reference against which to measure the strain introduced by the electronic asymmetry.  

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