Associate Professor
Canada Research Chair in Theoretical Chemistry and Chemical Biology
B.Sc. (Lipscomb), Ph.D. (UNC Chapel Hill)
My research concentrates on developing new theoretical, computational, and conceptual methods for understanding, predicting, interpreting, and quantifying chemical phenomena. Of particular interest are methods for modeling large and complex catalytic systems, whether they be enzymes, complex materials, or large molecules. Understanding how such catalysts work is part of the goal, but a more sweeping objective is to actually be able to “predict the products of chemical reactions”: Given a substrate and another reactant, catalyst, and molecular environment, what happens? Bang or whimper? Exothermic or endothermic? What is the product? What is the mechanism? How do you enhance the rate, yield, and specificity of the reaction?
To reach this goal, my research combines work on the underlying fundamental theory, developing new and more efficient computational techniques, and developing improved conceptual and semi-quantitative techniques for describing chemical reactions. Mostly I concentrate on density-functional theory, though I also toy with closely related methods using multi-particle electron densities (as the electron pair density) and density matrices (as the second order reduced density matrix). Among the virtues of density-functional theory (DFT) are low computational cost, relatively high accuracy, useful conceptual “descriptors” for the reactivity preferences of chemical reagents, and (speaking as a purist) its mathematical elegance. DFT’s biggest flaws are that, well, it isn’t fast enough to treat all the systems we’re interested in; it isn’t accurate enough for some systems; DFT-based reactivity descriptors don’t work all the time, and the fundamentals underlying DFT still aren’t completely understood. The way forward is clear: improve DFT’s computational efficiency (by improving existing “linear-scaling” algorithms, developing robust kinetic-energy functionals, and developing entirely new approaches); improve DFT’s accuracy (as by introducing non-locality into the exchange-correlation functional); develop improved DFT-based descriptors for chemical reactivity; and relentlessly pursue the problems in DFT’s theoretical foundations. My research touches on all these issues.
I also find myself moving into chemical dynamics, investigating new (and hopefully better) ways to locate, and then explore, reaction paths. Coming full circle, the goal is eventually to have methods for “predicting the products of chemical reactions” from knowledge of the reactants and reaction environment alone, without the need to know the products, or even the intermediates, in the chemical reaction.
An underlying philosophy of all these studies is a concern for the mathematical and physical fundamentals: I devote myself to the theory of computation complexity: when I develop a method, I want it to be “as efficient as possible” in a mathematically rigorous way; I try to combine the conflicting virtues of Davidson’s “the right answer for the right reason” and Percus’s “if it works, use it” maxims. (If it works, but you don’t know why, find out the reason: first find, and then study, the fundamental approximations on which the method is based; assess why these approximations should be valid and-that which is even more important-when they will fail.)
All my research combines all three facets of theoretical chemistry: mathematical studies of the underlying physical principles, the development of new computational methods, and applications to real chemical systems. Persons joining my group will be exposed to all three portions: mathematical derivation, method development, and computational studies-though some projects are “more theoretical” (and some are “more computational”) than others. As an affirmed “Parr-tisan”, coworkers are encouraged to pursue their own ideas and adapt my research projects to address their interests, use their abilities, and achieve their ambitions.
If you are interested in joining my research group or in possibilities for collaboration, you may wish to refer to my statement of research interests. Feel free to contact me if you have questions about my research, want to request a reprint, wish to collaborate, or are interested in joining my research group. Before contacting me, people interested in joining my research group may wish to refer to the appropriate guidelines.