Spin-coupled molecular orbitals: chemical intuition meets quantum chemistry

Understand

Molecular orbital theory is powerful both as a conceptual tool for understanding chemical bonding, and as a theoretical framework for ab initio quantum chemistry.

• Despite its undoubted success, MO theory has well documented shortcomings, most notably that it fails to correctly describe diradical states and homolytic bond fission.
• In this contribution, we introduce a generalised MO theory that includes spin-coupled radical states.
• We show through archetypical examples that when bonds break, the electronic state transitions between a small number of valence configurations, characterised by occupation of both delocalised molecular orbitals and spin-coupled localised orbitals.