A Hands‐On Guide to Open‐Shell Calculations in Organic Chemistry: Radical Chemistry, Single Electron Transfer, and Energy Transfer

Modern physical organic chemistry requires the use of computational tools, especially density functional theory (DFT) calculations, to understand the mechanisms behind organic transformations. Despite its numerous advantages, the use of DFT by experimental chemists is often hindered due to a lack of user‐friendly protocols. This challenge is particularly relevant when dealing with unpaired electrons, also known as open‐shell systems, which frequently appear as key intermediates in photoinduced transformations and radical chemistry, two powerful tools in organic methodologies. Herein, we present a set of DFT guidelines for the computation of photoredox and energy transfer (EnT) processes, aimed at non‐technical users, illustrated with representative case studies. Fundamental events commonly encountered in photoinduced reactions like halogen atom transfer (XAT), energy transfer (EnT), or minimum energy crossing point (MECP), among others, are discussed, and technical considerations are provided to facilitate the understanding of open‐shell mechanisms and the integration of these protocols into standard DFT calculation workflows.