Dr. Bess Vlaisavljevich

University of South Dakota
Department of Chemistry

Friday, September 23, 2022
12:00 Noon – Room 120 Meyerhoff Chemistry Building
HOST:  Dr. Joe Bennett

“Insights from Multireference Electron Correlation Methods in Transition Metal Chemistry”

Transition metal complexes contain sets of nearly degenerate orbitals in the valence space. While methods like density functional theory can often be used successfully, these complexes often contain so-called multiconfigurational electronic structure. This talk will include two examples where DFT methods break down and wave function based methods are required. The first family of complexes explored present a characteristic geometry change for systems ranging in size from 13 to 61 atoms. First, the metal ligand bond distance in Fe(II) spin-crossover complexes is elongated in the high spin state compared to the low spin state. The quality of the optimized geometry and its impact on the relative energies of the high spin and low spin state were assessed. Second, our work has moved beyond geometry optimizations to study the vibrational spectroscopy of chromium-chromium metal-metal bonds, which present prototypical examples of multiconfigurational electronic structures. We have explored three complexes and shown that good geometries can be obtained, although the choice of CASPT2 zeroth-order Hamiltonian is important. The Raman active metal-metal and metal-ligand stretching modes are computed allowin comparisons with isotope labeling experiments to be made. The effect of anharmonicity is also explored by normal mode sampling. Comparisons with density functional theory are made in all cases.