title: Electronic structure of N₂P₂ four-membered rings.
abstract: The biradicaloid character of the ground-state structures of N2P2 rings is studied by using the high-level ab initio multiconfigurational CASPT2/CASSCF method. In order to obtain accurate descriptors, we combine two criteria: 1) singlet-triplet energy gaps and 2) relative values of the occupation numbers for bonding and antibonding orbitals associated with the radical sites. The singlet-triplet energy gaps, the occupation numbers of antibonding-like orbitals, and the weights of the main configuration state functions (CSFs) of the ground-state wavefunctions, that is, Ψ((1)A1), are used to derive the biradicaloid character that ranges from 10-15%.
authors.affiliation: Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr (Germany). escudero@kofo.mpg.de.
authors.forename: Daniel
authors.initials: D
authors.lastname: Escudero
authors.forename: Antonio
authors.initials: A
authors.lastname: Frontera
authors.forename: Rainer
authors.initials: R
authors.lastname: Streubel
keywords: ab initio calculations; biradicaloids; bonding; heterocycles; main group elements