Exchange coupling interactions between open-shell ions in polynuclear transition-metal complexes define key magnetic and spectroscopic properties of these systems. The metal coordination environment, especially the bridging ligands, determine the nature and magnitude of the magnetic coupling. The interpretation of experimental data is guided by fits to phenomenological models, and is often supported by density functional theory (DFT), in particular broken-symmetry DFT (BS-DFT). However, the quality of the theoretical predictions with BS-DFT strongly depends on the density functional chosen and thus relies on extensive calibration studies. Moreover, BS-DFT is not systematically improvable and can only predict the sign and total span of spin ladders but not the exact nature of the magnetic coupling paths. <br/>Multireference quantum-chemical calculations are in principle capable of describing each individual spin state arising from magnetic coupling of open-shell ions. With the advent of density matrix renormalization group (DMRG) the description of realistic systems with multiple centers and many unpaired electrons has become viable. DMRG thus has the capacity to provide a thorough understanding of the magnetic coupling mechanisms in experimentally relevant transition metal complexes.<br/>Here, we present a simple tool that allows us to identify exchange coupling pathways in polynuclear transition metal complexes from a wave function constructed in a polarized pseudo atomic orbital basis. This tool is based on an entanglement analysis of the interacting orbitals in the DMRG wave function. The orbital entanglement analysis constitutes a visually intuitive comparison of the magnetic interactions among different coordination environments. The capabilities of the entanglement analysis are showcased with a series of manganese dimers with different bridging ligands.

Orbital entanglement analysis of exchange-coupled transition-metal complexes

2019 Fall National Meeting

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