Following the evolution of excited states along photochemical reaction pathways

Analyzing the behavior of potential energy surfaces (PESs) of diabatic excited states (ESs) becomes of crucial importance for a complete understanding of complex photochemical reactions. Since the definition of a compact representation for the transition density matrix, the use of the natural transition orbitals (NTOs) has become a routine practice in time‐dependent density functional theory calculations. Their popularity has remarkably grown due to its simple orbital description of electronic excitations. Indeed, very recently, we have presented a new formalism used for the optimization of ESs by tracking the state of interest computing the NTO's overlap between consecutive steps of the procedure. In this new contribution, we generalize the use of this NTO's overlap‐based state‐tracking formalism for the analysis of all the desired diabatic states along any chemical reaction pathway. Determining the PES of the different diabatic states has been automatized by developing an extension of our recently presented algorithm, the so‐called SDNTO: “Steepest Descent minimization using NTOs.” This automatized overlap‐based procedure allows an agile and convenient analysis of the evolution of the ESs avoiding the intrinsic ambiguity of visualizing orbitals or comparing physical observables. The analysis of two photochemical reactions of the same nature with different PES landscapes perfectly illustrates the utility of this new tool. The characterization of diabatic state potential energy surfaces (PES) is important for a better understanding of photochemical reactions. An extension of the recently developed natural transition orbital‐based optimization algorithm allows a convenient analysis of the evolution of the different excited states throughout a photochemical reaction pathway. Two molecular systems presenting excited state intramolecular proton transfer with different PES landscapes have been used to exemplify the capabilities of the new developed tool.