Ru L2,3 XANES theoretical simulation with DFT: A test of the core-hole treatment

Density functional theory (DFT)-based relativistic calculations were performed to model the Ru L-edge X-ray absorption near edge structure (XANES) spectra of the hexaammineruthenium complex [Ru(NH3)6]3+ and “blue dimer” water oxidation catalyst, cis,cis- [(bpy)2(H2O)RuIIIORuIII(OH2)(bpy)2]4+ (bpy is 2,2-bipyridine). Two computational approaches were compared: simulations without the core-hole and by modeling of the core-hole within the Z+1 approximation. Good agreement between calculated and experimental XANES spectra is achieved without including the core-hole. Simulations with algorithms beyond the Z+1 approximation were only possible in a framework of the scalar relativistic treatment. Time-dependent DFT (TD-DFT) was used to compute the Ru L-edge spectrum for [Ru(NH3)6]3+ model compound. Three different core-hole treatments were compared in a real-space full multiple scattering XANES modeling within the Green function formalism (implemented in the FEFF9.5 package) for the [Ru(Mebimpy)(bpm)(H2O)]2+ complex. The latter approaches worked well in cases where spin–orbit treatment of relativistic effects is not required.

► Effect of the core-hole on the Ru L2,3-edge spectra of Ru complexes was modeled with DFT, TD-DFT and MS.
► Results of the ground state relativistic DFT calculations are in a good agreement with experiment.
► Z+1 approximation for core-hole effect did not improve agreement with experiment.
► TD-DFT for open shell was only possible with the scalar approach and yielded an averaged L2,3-edge spectrum.
► Addition of core-hole treatment in FEFF improved agreement with experiment for Ru d6 complex.