David Yarkony

David Yarkony

D. Mead Johnson Professor of Chemistry

Remsen 310
410-516-4663
yarkony@jhu.edu
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David R. Yarkony was born in New York City. He graduated from State University of New York at Stony Brook, with a Bachelor of Arts in chemistry, summa cum laude, in 1971. He received his Ph. D. in chemistry from the University of California at Berkeley in 1975, with H. F. Schaefer III and after two years at the Massuchusetts Institute of Technology working with Robert J. Silbey on temperature effects on excitons and exciton transport, he joined the faculty at Johns Hopkins University in 1977. He was promoted to full professor in 1984 and is currently the D. Mead Johnson Professor of Chemistry.

Professor Yarkony has been interested in nonadiabatic chemistry since 1985 when he, in collaboration with Byron Lengsfield and Paul Saxe, reported to a unique algorithm for determining the first derivative or momentum coupling for multireference configuration interactions wave function using analytic gradient techniques. This lead Yarkony, in the 1990's to develop algorithms to locate and characterize conical intersections of states of the same symmetry. These algorithms have shaped his career as he and several other groups have demonstrated that such conical intersections are ubiquitous and must be considered in any ultrafast nonadiabatic process.

More recently Yarkony has turned his attention to the effects of conical intersections on photoelectron spectra and photodissociation. Here a key issue is the accuracy of the adiabatic electronic structure data, energies, energy gradients and derivative couplings, used in the simulations. Yarkony, with Michael Schuurman (bound molecules) and Xiaolei Zhu (dissociative species) have developed algorithms to construct accurate quasi-diabatic representation of high level electronic structure data. These algorithms are having a major impact on the accuracy with which nonadiabatic processes can be simulated.

Theoretical Studies of Electronically Nonadiabatic Processes

According to the Born-Oppenheimer approximation nuclei move on a single potential energy surface created by the faster moving electrons. This approximation is at the heart of our description of most chemical processes. From protein folding to tribology to catalysis the Born Oppenheimer approximation rules. So why study nonadiabatic processes, processes in which the Born-Oppenheimer approximation breaks down. The answer is simple in the absence of nonadiabatic processes life on earth as we know it would not exist. Light harvesting, vision, DNA photostability and a variety of essential upper atmospheric processes depend on electronically nonadiabatic steps.

Of course this has been known for decades. What is unusual and exciting is that our way of thinking about electronically nonadiabatic processes has changed, and change dramatically. The changing face of nonadiabatic chemistry is the consequence of a rethinking of the role of surface intersections ( conical intersections) of states of the same symmetry in these processes. Once little more than a theoretical curiosity today conical intersections of two (or more) states of the same symmetry are now understood to be an essential aspect of nonadiabatic processes. This change in paradigm can dramatically change the predicted/expected rate of a nonadiabatic process.

My research group has helped lead this revolution. We have developed the tools for studying conical intersections that define the state of the art in this area and as a result have lead the way in advancing the computational description of this singular consequence of the separation of nuclear and electronic time scales.

Recent advances in full dimensional quantum mechanical descriptions of nonadiabatic processes, combined with a unique algorithm we have developed for constructing quantifiably quasi-diabatic representations of accurate adiabatic electronic structure data will enable simulations of nonadiabatic processes with unparalleled accuracy. We have used this capability to uncover a decade old misconception in ammonia photodissoication and have extended the algorithmic capacilities to determine quasi-diabatic representations for much larger system which will open whole new directions for studies of nonadiabatic phenomena.

In summary nonadiabatic chemistry is an important field with a bright new future and we expect to play a leading in this area.

Coupled Potential Energy Surfaces

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