Spin state relaxation of iron complexes: The case for OPBE and S12g

The structures of nine iron complexes that show a diversity of experimentally observed spin ground states were optimized and analyzed using the Density Functional Theory (DFT). An extensive validation study of the new S12g functional was performed, with a discussion concerning the influence of the environment, geometry and its overall performance based on a comparison with the well-proven OPBE functional. The OPBE and S12g functionals gave the correct spin ground state for all investigated iron complexes. Since S12g performs remarkably well, it could be considered a reliable tool for studying the energetics of the spin state in complicated transition metal systems.