Electron invariants and excited state structural analysis for electronic transitions within CIS, RPA, and TDDFT models

Abstract

AbstractWe revisit the interpretative scheme (Luzanov et al., Theor Exp Chem 1974, 10, 354) of singly excited configuration interaction (CIS) model given earlier at semiempirical level. Detailed computations and spectral (natural orbital) treatment of the CIS density matrices of various types are presented. The corresponding hole‐particle densities and related excitation localization indices are described. All the quantities are extended to the excited states calculated in the random phase approximation and closely related time‐dependent density functional theory (TDDFT). The localization indices and charge transfer numbers which are invoked to describe interfragment interactions provide a basis for our scheme which is referred to as the excited state structural analysis for electronic transitions. The proposed analysis is exemplified by various moderate and large‐size conjugated molecules treated within ab initio TDDFT and the Parizer–Parr–Pople approximation. Finally, we propose a possible generalization to the electronic transitions between CIS‐like states followed by applications to singlet organic biradicals treated within the π‐electron spin‐flip CIS. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010