First-Principles Simulations of an X-ray Absorption Probing Redox Doping Single-Molecule Magnet.

We present fully ab initio simulations of Fe L-edge X-ray absorption spectroscopy (XAS) for archetype single-molecule magnet tetrairon Fe4 using a linear-response time-dependent density functional theory with a spin-orbit coupling scheme. In particular, electronic and structural modifications in the Fe4 core, as induced by Li doping and by the change of R (-H and -C5S·), were studied by systematically benchmarking hybrid functionals and basis sets. A parameter-free computational protocol is, therefore, established, which reproduces experimental spectra with excellent agreement. The simulations capture key spectroscopic signatures, including L3-L2 splitting, redox-induced shifts upon Li doping, and the robustness of spectral shapes against magnetic coupling schemes and structural distortions. This study establishes a practical and accurate framework for simulating 2p XAS in complex magnetic molecules, providing valuable insight into their electronic behavior and enabling a rigorous connection between experiment and theory.