Quantifying the Nature of Lone Pair Domains

The lone pair lies at the heart of chemistry, and is often in a conceptual respect the site of chemical reactivity. Here we show how the analysis of the electron localization function (ELF) can be improved upon by introducing intra-basin partitioning. The high-ELF localization domain population (HELP), is presented as a probe of the more chemically relevant and electron-localized regions of the ELF lone pair basin, and shown to correlate with a range of physical properties and quantum mechanical constructs, such as the ESP, e and H+ affinity, IP, HOMO/LUMO energies, atomic charge, NBO lone pair orbitals, and molecular geometry. A strong connection between topological density and orbital-based analysis of chemistry is intuitively expected, yet this is the first time that an average electron population, obtained by any localization method, can be linked to properties of molecules. The application of HELP as a descriptor of lone pair domains is predicted to be of general use.