Localized molecular orbitals for excited states n→π* (CO) excitation

A one-particle density matrix method to generate directly localized orbitals dedicated to multireference wave functions has been recently developed. In this work we apply this formalism to generate local complete active space self-consistent field (CAS-SCF) orbitals for excited states. We have focused our attention on the singlet n→π* (CO) excited state in conjugated systems. At convergence the doubly occupied and virtual valence orbitals are localized. The single occupied π* (CO) orbital is partly delocalized over some carbon atoms, even though the delocalization tail is not extended in all the molecule. The quality of the orbitals has been tested by comparing the excitation energies by using local orbitals with those obtained by using ‘classical’ delocalized CAS-SCF orbitals.