BPT pseudo-forces

For the chemical shift it turns out that it can be expressed in terms of the atomic polarization energy. Expanding it with respect to the chemical shift tensor around the experimental value and taking the gradient, the BPT pseudo-force can be deduced... 

These calculations demonstrate that it is possible to obtain highly refined structures using chemical shift pseudo-forces. The resulting differences between measured and calculated BPT chemical shifts are in the range of the experimental error. BPT pseudo-forces are in the same range as electrostatic interactions, and they act on all atoms that contribute to the chemical shift of a site. 

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