Localized Intrinsic Valence Virtual Orbitals as a Tool for the Automatic Classification of Core Excited States

Accurate assignments of the unoccupied
molecular orbitals involved
in electronic excitations are crucial to the interpretation of experimental
spectra. Here we present an automated approach to the orbital assignment
of excited states by introducing a unique orbital basis known as localized
intrinsic valence virtual orbitals (LIVVOs), which are a special case
of the previously reported valence virtual orbitals. The LIVVOs are
used to quantify the local contributions to particle orbitals from
orthogonality-constrained density functional theory, providing an
assignment with atomic-level/angular momentum shell specificity. This
localized set also allows us to define the total valence character
of an excited state. We highlight the utility of our approach by studying
the local orbital changes in core-excited states at the sulfur K-edge
of ethanethiol and benzenethiol as well as the oxygen K-edge spectrum
of the water monomer and dimer.