Dr. Mark R. Hoffmann
Chester Fritz Distinguished ProfessorB.A., 1980, Northwestern University; Ph.D., 1984, University of California- Berkeley; Postdoctoral Research Associate, 1985-86, University of Chicago; Postdoctoral Research Associate, 1986-88, University of Utah.
My group performs research in theoretical and computational physical chemistry, and is focused on the development and use of novel ab initio methods of molecular electronic structure theory for studying ground and excited potential energy surfaces (PES). Our current research interests include: multireference and quasidegenerate perturbation theory descriptions of electron correlation; high and ultrahigh accuracy descriptions of the electronic structures of difficult small- to moderate-sized molecules and molecular ions; and studying the effects of a nanoscale background on the physical and chemical properties of a molecular-system-sized moiety. Using these techniques, and other more conventional approaches where appropriate, we have recently investigated highly strained systems, such as [3,3’] bidiazirinylidene (C2N4), which has relevance to the development of High Energy Density Materials (HEDM), and a variety of atmospherically important oxides, such as NO-. We are studying metal containing molecules, such as the cobalt dimer (Co2), and molecular ions in an effort to assist in the development of new catalytic materials. As an extension of our work on environmental effects on molecular electronic structure, we have investigated the behavior of molecules in intense electromagnetic fields, which has the promise of controlling molecular reactions in ways otherwise not possible. We often collaborate with other theorists across the globe and have strong interactions with several experimental groups.
Our primary framework for developing new methods for electronic structure theory is through hybrid variational-perturbational theories, e.g. quasidegenerate perturbation theory (QDPT). This framework is desirable because of both the need for good long-range correlation of electronic structure (i.e. mean field approximations (e.g., SCF) are often not adequate, especially near transition states) and good short-range correlation. Traditional methods of including short-range electron correlation, such as configuration interaction (CI) or coupled cluster (CC), have prohibitive algorithm scaling with the number of electrons in the system. Our results show that a well-constructed second-order perturbation theory, such as our Generalized Van Vleck-based approach, can give near chemical accuracy over wide regions of the relevant potential energy surfaces (PESs) at a substantial computational resource savings relative to traditional methods, provided that the long-range electron correlation is described correctly. We are exploring extensions to our theory for larger molecules and clusters by embedding wave function descriptions in density functional theory (DFT) descriptions of the environment, which may be good representatives of catalytically active surfaces. Recently, we have made progress on the ability to describe simultaneously multiple PESs to investigate the coupling of Born-Oppenheimer surfaces.
1. Khait, Y. G.; Theis, D.; Hoffmann, M. R. Lagrangian approach for geometrical derivatives and nonadiabatic coupling terms in MRCISD. Mol. Phys. 2010, 108, 2703-2716.
2. Khait, Y. G.; Jiang, W.; Hoffmann, M. R. On the inclusion of triple and quadruple electron excitations into MRCISD for multiple states. Chem. Phys. Lett. 2010, 493, 1-10 [Frontiers Article].
3. Bongfen Mbote, Y. E.; Khait, Y. G.; Hardel, C.; Hoffmann, M. R. Multireference Generalized Van Vleck Perturbation Theory (GVVPT2) Study of the NCO + HCNO Reaction: Insight into Intermediates. J. Phys. Chem. A 2010, 114, 8831-8836.
4. Khait, Y. G.; Hoffmann, M. R. Embedding theory for excited states, J. Chem. Phys. 2010, 133, 044107/1-6.
5. Mokambe, R. M.; Khait, Y. G.; Hoffmann, M. R. Ground and Low-Lying Excited Electronic States of [3,3’] Bidiazirinylidene (C2N4), J. Phys. Chem. A 2010, 114, 8119-8125.
6. Shao, P.; Li, Y.; Azenkeng, A.; Hoffmann, M. R.; Sun, W. Influence on Alkoxyl Substituent on 4,6-Diphenyl-2,2’-bipyridine Ligand on Photophysics of Cyclometalated Platinum(II) Complexes: Admixing Intraligand Charge Transfer Character in Low-Lying Excited States. Inorg. Chem. 2009, 48, 2407-2419.
7. Jiang, W.; Khait, Y. G.; Hoffmann, M. R. MRCISD and GVVPT3 study of the low-lying electronic states of NO-. Mol. Phys. 2009, 107, 889-897.
8. Nichols, P.; Hoffmann, M. R. A momentum-conserving Franck-Condon approximation: Theory and application to the photodissociation of Li2+ in an intense laser field. J. Chem. Phys. 2008, 128, 044115/1-7.
9. Azenkeng, A.; Laumb, J. D.; Jensen, R. R.; Olson, E. S.; Benson, S. A.; Hoffmann, M. R. Carbene Proton Attachment Energies: Theoretical Study. J. Phys. Chem. A 2008, 112, 2677-2682.
10. Wang, H.; Kais, S.; Aspuru-Guzik, A.; Hoffmann, M. R. Quantum Algorithm for Obtaining the Energy Spectrum of Molecular Systems. Phys. Chem. Chem. Phys. 2008, 10, 5388-5393.