Real-Space Electron Correlation Descriptors

Overview

A key insight driving our research is that the statistics of the electron number distribution in real-space atomic basins contain rich information about electron correlation and chemical bonding.

By computing the probability of finding n electrons in basin Ω, we obtain:

• The average electron population N(Ω) — the QTAIM atomic charge.
• The variance — a measure of electron fluctuation and localisation.
• The delocalization index δ(A,B) — the covariance of electron populations between basins A and B, providing an orbital-invariant bond order.
• Higher-order cumulants — sensitive to multi-centre bonding and electron correlation beyond mean-field.

Non-Covalent Interactions

We use delocalization indices, variance maps, and IQA inter-atomic energies to characterise and classify non-covalent interactions (hydrogen bonds, halogen bonds, van der Waals, π–π stacking) without reference to molecular orbitals.

Beyond DFT

Our descriptors are applicable with any level of theory (HF, DFT, CISD, CCSD, CASSCF, Quantum Monte Carlo), allowing direct assessment of the effect of electron correlation on bonding descriptors.