Our group's research is focused on the development and use of novel methods of electronic structure theory for the elucidation of ground and excited potential energy surfaces (PES). Included in our current research interests are the high and ultrahigh accuracy descriptions of the electronic structures of small- to moderate-sized molecules and molecular ions; the relation of unusual PES and moderate- to high-energy vibrational motion, and possible subsequent translational motion, is of particular interest. We have recently investigated difluorodioxirane (CF2O2) and difluorodiazirine (CF2N2), which have relevance to the development of High Energy Density Materials (HEDM), and a variety of atmospherically important oxides. We are studying metal containing molecules and molecular ions in an effort to assist in the development of new catalytic materials.

We have an ongoing interest in the development of hybrid variational-perturbational theories, e.g. quasidegenerate perturbation theory (QDPT), for the description of electron correlation. Mean field approximations [e.g., SCF, and even multiconfigurational SCF (MCSCF)], are not always adequate to describe molecules well, especially near their transition states. Traditional methods of including 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 at a substantial saving relative to traditional methods, provided that the nondynamic electron correlation is described correctly. We are exploring extensions to our theory for larger molecules and eventually clusters, which may be good representatives of catalytically active surfaces. Recently, we have made progress on using the ability of QDPT to describe simultaneously multiple PES to investigate coupling of Born-Oppenheimer surfaces.

REPRESENTATIVE PUBLICATIONS

"Perturbative triple and quadruple excitation corrections to MRCISD", Y. G. Khait, J. Song, and M. R. Hoffmann, Chem. Phys. Lett., 2003, 372, 674–685.

"Optimization of MCSCF Excited States Using Directions of Negative Curvature", M. R. Hoffmann, C. D. Sherrill, M. L. Leininger, and H. F. Schaefer III, Chem. Phys. Lett., 2002, 355, 183–192.

"Finite Element Method for Two-Dimensional Vibrational Wave Functions: Theory and Application to van der Waals Molecules", T. J. Dudley, R. R. Pandey, P. E. Staffin, M. R. Hoffmann, and G. C. Schatz, J. Chem. Phys ., 2001, 114, 6166–6179.