Special Issue Preface pubs.acs.org/JPCA
Tribute to David R. Yarkony spin−orbit interaction from the Breit−Pauli Hamiltonian for general molecular problems involving general CI wave functions, or in the development of general approaches to efficiently locate and optimize points of degeneracy between two or more electronic states of the same symmetry. Each of these examples shows that it is generally necessary to expand the toolbox of available theoretical and computational methods before engaging with novel families of research problems. David’s rigorous mathematical approach, coupled with detailed knowledge of accurate electronic structure methods, has resulted in the delivery of powerful tools in computational chemistry However, ultimately, this effort is a means to an end, namely, the study of actual problems in quantum chemistry, spectroscopy, and nonadiabatic dynamics. Sherlock Holmes stated that “It is a capital mistake to theorize before one has data”, and with efficient algorithmic tools and computer resources, data need not be a concern for most problems in computational chemical physics. What is often in short supply, though, are the requisite concepts that educate our intuition for various molecular processes. The final component characterizing David’s research career is taking computational results on “real” molecules using “real” ab initio methods and articulating them in terms of precisely those concepts that influence our intuition. The ability to predict the spectroscopic signature of spin−orbit coupling in polyatomic molecules, and making contact with experimental observables generally, informs the interpretation of the measured results. The ability to actually locate and describe continuous seams of conical intersection in the excited-state potential energy surfaces of molecules both illustrates their ubiquity and highlights their prevalence in ultrafast nonadiabatic transitions, thereby impacting our intuition on internal conversion processes in chemistry. The quantitative description of the topography of the potential energy surfaces in the vicinity of a point of degeneracy has influenced our thinking regarding complex wave packet dynamics through a conical intersection. These conceptual developments are arguably the important outcome from any scientific inquiry. We who have worked most closely with David through the years have appreciated not only his profound physical insights, which have fundamentally shaped how we think about these areas of chemical physics, but also his unique sense of humor and a generosity of spirit that primarily manifested as the patience to explain concepts as many times as was necessary. We are looking forward to see what new areas of theoretical chemistry will warrant David’s attention.
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t is our pleasure to celebrate the seminal contributions of David Yarkony to the development of computational theoretical chemistry in this special section of The Journal of Physical Chemistry A. While David’s work continues to have a significant impact in numerous areas of theoretical chemistry, the central thrust of his research program has led to dramatic advances in the elucidation of nonadiabatic chemical processes. That David’s efforts on the characterization (and popularization) of conical intersections in excited-state processes have impacted how we think about internal conversion in molecules gives evidence to the considerable influence his work has had on a generation of physical chemists. David left his native Brooklyn, New York and crossed the country to begin graduate studies at UC Berkeley with Henry F. Schaefer, III, in 1971. Following a postdoctoral position with Robert J. Silbey at MIT, (1975−1977), David became an Assistant Professor at Johns Hopkins University, where he has been ever since. If one attempts to take a global view of David’s career to this point, a distinctive approach to problem solving clearly emerges. The initial stage of his investigatory process is characterized by a genuine interest in a question of chemical physics that requires nonexistent or underdeveloped theoretical and computational tools. Subsequently, David will work to first build a computational infrastructure that can adequately address these problems. Given his mathematical inclinations, part of this development will entail the derivation of formal treatments with which we’re all now familiar. However, from the start of his research career, which auspiciously coincided with the advent of general purpose computer resources, David has participated in the development of quantum chemistry as a computational discipline. Thus, formal derivation has as its ultimate fate computational implementation. Examples of this dynamic at work can be found in David’s (and co-workers) ground-breaking work on the computation of nonadiabatic coupling matrix elements using gradient formalisms developed for configuration interaction (CI) and multireference self-consistent field (MCSCF) wave functions, workhorses for the description of molecular excited electronic states, or in the development of algorithms to employ the © 2014 American Chemical Society
Spiridoula Matsika Henry F. Schaefer, III Michael S. Schuurman
Special Issue: David R. Yarkony Festschrift Published: December 26, 2014 11837
dx.doi.org/10.1021/jp512064b | J. Phys. Chem. A 2014, 118, 11837−11837
