The binatural orbitals of electronic transitions

Abstract

The well-known natural orbitals are defined as eigenfunctions of a one-particle reduced density operator, and can be obtained from a computed density matrix by diagonalization. Similarly, in this article we define the binatural orbitals, which are obtained for a pair of wave functions by a singular value decomposition of a reduced transition density matrix. The pair of states would usually be eigenstates of the electronic Hamiltonian, and the binatural orbitals then serve as a useful tool for the analysis of the transition between these states. More generally, application to any two state functions gives important information as to how the two states differ. Some examples are shown.

Keywords:

• binatural orbitals
• electron transitions
• electron correlation
• RASSI
• MOLCAS

Acknowledgements

PÅM thanks the Swedish National Science Foundation for financial support via the Linnaeus grant for the Organizing Molecular Matter centre of excellence project (239-2009-6794), and through individual grant (2010-5008).