Excited electronic states of transition-metal dimers and the VBCI model: an overview

Applications of the Valence-Bond Configuration Interaction (VBCI) model to the electronic structure of transition-metal dimers are reviewed. This appr oach describes the shifts and splittings of ground and excited electronic s tates within a configuration interaction scheme. In particular, it allows a correlation of the magnetic properties of the electronic ground state (fer ro- or antiferromagnetic coupling) to shifts and splittings in excited (and ligand-field) charge-transfer states which can be probed by optical absorp tion spectroscopy and magnetic circular dichroism. The review correlates th e VBCI description to earlier approaches to describe dimer interactions (co upled-chromophore model, Tanabe-model, transition-dipole vector coupling) a nd makes the connection to the treatment of mixed-valent systems. (C) 2001 Elsevier Science B.V. All rights reserved.