Visualizing electronic excitations with the particle-hole map: orbital localization and metric space analysis

The particle-hole map (PHM) is a computational tool to visualize electronic excitations (calculated using time-dependent density-functional theory), based on representations in canonic molecular orbital transition space. Beyond the standard canonical representation, transformation to localized orbitals is a common technique in electronic structure theory. We analyze the PHM as a visualization tool for both canonical and localized molecular orbital representations in various inorganic and organic charge-transfer complexes. We show that the canonical and localized PHMs can be used to construct simple descriptors of the charge-transfer character of an excitation through metric space analysis.