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.