The EDDB method relies on the following decomposition of the one-electron densityED(r):
EDLA(r) - Density of Electrons Localized on Atoms (electrons that do not parcicipate in covalent bonding);
EDLB(r) - Electron Density of Localized Bonds (electrons shared by no more than two atoms);
EDDB(r) - Electron Density of Delocalized Bonds (electrons shared by more than two atoms e.g. in aromatic rings).
Features & Capabilities
The EDLB(r) and EDDB(r) functions provide a uniform approach to quantify chemical bonding and resonance, multicenter electron sharing and aromaticity within one theoretical paradigm. There are several important features that set EDDB apart from other aromaticity indices:
EDDB does not suffer from the ring-size extensivity issue (in contrast to e.g. NICS and MCI);
EDDB can be used to study any aromatic system regardless of its size and topology (in contrast to e.g. NICS,X and PDI);
EDDB does not depend upon parametrization to the reference model system (in contrast to e.g. HOMA and FLU);
EDDB usually performs similarly to MCI but is much less computationally expensive;
The results of the EDDB analyses are much easier to interpret than e.g. MCI and FLU.
At the moment the EDDB method works for one-determinant wavefunctions (HF- and DFT-type) of both closed- and open-shell molecular systems; generalization of the EDDB method for the post-HF wavefunctions is in progress. Its current implementation involves the Hilbert-space partitioning within the representation of natural atomic orbitals (NAO), which is widely available for most of the popular quantum-chemistry packages through NBO and JaNPA interfaces.
Global resonance effects in DNA fragment AATTCGTATAAAAACTAGAC visualized by EDDBg(r):