Excitation Energies for Transition Metal Compounds from Time-Dependent Density Functional Theory. Applications to MnO4-, Ni(CO)4, and Mn2(CO)10

The first time-dependent density functional theory (TDDFT) calculations on the spectra of molecules containing transition metals are reported. Three prototype systems are considered, of which the assignments are controversial:  MnO4-, Ni(CO)4, and Mn2(CO)10. The TDDFT results are shown to be comparable in accuracy to the most elaborate ab initio calculations and lead to new insights in the spectra of these molecules. In some cases, the presented TDDFT results differ substantially, in both the ordering and the values for the excitation energies, from the older DFT method for the calculation of excitation energies:  the ΔSCF approach. For the Mn2(CO)10 molecule, the presented results are the highest-level theoretical results published so far. Over all, the results show that TDDFT can be a very useful tool in the calculation and interpretation of the spectra of transition metal compounds.