Qualitative Understanding and Decomposition Schemes

It is obvious from the discussion in the last sections that the evaluation of distributed multipoles and polarizabilities is not straightforward and also time consuming. In particular, for routine investigations of large extended assemblies it is desirable to have easily obtainable descriptors for local interaction patterns at hand. 

None of this can be detected by standard geometric criteria. First-principles simulations like CPMD allow for new wave-function-based descriptors [231] as the electronic structure is - in addition to the positions of all atomic nuclei involved -available on the fly . Of course, the above mentioned fundamental problem that the interaction energy is not an observable quantity is in first-principle simulations as apparent as in static calculations. However, the wavefunction naturally tracks all electronic changes in an aggregate. A wavefunction-based descriptor would also be helpful in traditional molecular dynamics because snapshots can be calculated with advanced static quantum chemical methods. 

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