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With the aim of offering new computational tools helping in the description of photochemical reactions and phenomena occurring at the excited state, we present in this work the capability of a density based index (Π) in locating decay channels from higher to lower excited states. The Π index, previously applied to disclose non-radiative decay channels from the first excited state to the ground state, is very simple in its formulation and can be evaluated, practically with no extra computational cost, and coupled to any quantum method able to provide excited states densities. Indeed, this index relies only on the knowledge of energetics and electron densities of the different electronic states involved in the decay. In the present work, we show the proficiency of the Π index in the general case of decay between excited states by applying it to two model systems well characterized both theoretically and experimentally. In both cases, this descriptor was successful in spotting the regions where excited states are more likely to decay, thus suggesting its potential interest for further application in the design of new compounds. © 2018 Wiley Periodicals, Inc., (© 2018 Wiley Periodicals, Inc.)

With the aim of investigating qualitatively and quantitatively the impact of using excited state relaxed or unrelaxed density for the estimation of nature and characteristic of electronic excited states, we analyzed the behavior of 52 exchange correlation functionals for the prediction of density-based indexes such as those recently introduced in literature to evaluate the charge transfer distance (D CT ) (Le Bahers et al. J. Chem. Theory Comput. 2011, 7, 2498) in the case of a prototype family of push-pull dyes. Our results show that while a qualitatively consistent assessment of the nature of the excited states is obtained using either the unrelaxed or the relaxed density, from a quantitative standpoint we observe large discrepancies in the charge transfer distance for electronic transitions having substantial CT character. This behavior is independent of nature of the exchange-correlation functional used. © 2018 Wiley Periodicals, Inc., (© 2018 Wiley Periodicals, Inc.)

This work presents a new index, M AC , enabling the on-the-fly detection of ghost charge transfer (CT) states, a major problem in time-dependent density-functional theory calculations. This computationally inexpensive index, derived as a modification of the Mulliken estimation of transition energy for CT excitations, relies on two basic ingredients: an effective CT distance, computed using our density-based index (D CT ), and an orbital weighted estimation of the Ionization Potential and Electron Affinity. Some model systems, representative of both intermolecular and intramolecular CT excitations, were chosen as test cases. The robustness of our approach was verified by analyzing the behavior of functionals belonging to different classes (GGA, global hybrids and range separated hybrids). The results obtained show that ghost states are correctly spotted, also in the delicate case of intramolecular excitations displaying substantial donor-bridge-acceptor delocalization, in a regime for which the standard Mulliken formulation attends its limits. © 2017 Wiley Periodicals, Inc., (© 2017 Wiley Periodicals, Inc.)