Physical/Theoretical Chemistry Seminar: Gerald Knizia, Pennsylvania State University (Host: Todd Martinez)
About the Seminar
"Revealing the chemistry in quantum chemistry with local orbitals"
With quantum chemistry, nowadays most physical properties of molecules can be easily and (often) accurately calculated—for example, DFT calculations of molecular structure and reaction paths have become routine complements to organic and inorganic chemistry. However, the techniques used in these calculations afford no easy way of "making sense" of the bonding mechanisms behind the computed quantities.
Additionally, many central empirical concepts of chemistry, including concepts as basic as partial charges, bond orders, and even covalent bonds themselves, have no consensus physical definition.
We here argue that, once we define physically sound "atomic orbitals" in a molecule, quantities representing most other empirical concepts can be straight-forwardly derived from simple physical arguments, and then easily calculated. In this sense, we show how our Intrinsic Atomic Orbital (IAO) technique gives rise to partial charges and bond orders, and to Intrinsic Bond Orbitals (IBOs) which exactly represent DFT wave functions yet correspond to the electron pairs of Lewis structures (e.g., σ- and π-bonds). Even curly-arrow reaction mechanisms can be readily derived!
Based on selected examples, we show how IAOs and IBOs allow the analysis of bonding in both well-known and novel or exotic chemical species, and how the method played a key role in understanding metal-catalyzed reaction mechanisms.
About the Speaker
Gerald Knizia is a theoretical chemist, focusing on the theory, methods, and algorithms of molecular electronic structure, and is one of the main authors of Molpro. Originally trained as a physicist, he fell for quantum chemistry while preparing his master's thesis under the supervision of Peter Fulde at MPI-PKS in Dresden. After graduating from TU-Dresden in 2006, he joined the group of Hans-Joachim Werner at the University of Stuttgart. There he researched explicitly correlated electronic structure methods (RMP2-F12, CCSD(T)-F12), which are now widely used for high-accuracy computational thermochemistry, graduating in 2010. In 2011, Gerald joined the group of Garnet Chan in Cornell, where both developed the Density Matrix Embedding Theory (DMET), a "divide & conquer"-approach to tackle complex strongly correlated systems. Since 2015 Gerald is an Assistant Professor of Chemistry at the Pennsylvania State University. In this capacity, his research is focused on methods for the discovery, analysis, and interpretation of chemical reaction mechanisms.