Understanding Radicals via Orbital Parities

TL;DR

This paper introduces orbital parity analysis as a novel method for understanding radicals, enabling visualization and classification based on spin distribution and radical character through density matrix evaluation.

Contribution

It presents a new approach using orbital parities derived from density matrices to analyze radical character and classify radicals based on spin-site separability.

Findings

Orbital parity analysis effectively visualizes excess spin in radicals.

The method classifies radicals based on spin-site separability.

Application to polyradicals and bond breaking demonstrates its utility.

Abstract

We introduce analysis of orbital parities as a concept and a tool for understanding radicals. Based on fundamental reduced one- and two-electron density matrices, our approach allows us to evaluate a total measure of radical character and provides spin-like orbitals to visualize real excess spin or odd electron distribution of singlet polyradicals. Finding spin-like orbitals aumotically results in their localization in the case of disjoint (zwitterionic) radicals and so enables radical classification based on spin-site separability. We demonstrate capabilities of the parity analysis by applying it to a number of polyradicals and to prototypical covalent bond breaking.