NSF Award
2422858
Joseph Subotnik of Princeton University is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry to develop new methods for modeling the flow of energy between electrons, nuclei, and spin. Understanding exactly how energy flows between these fundamental particles is essential for understanding how nature designs efficient pathways to convert one form of energy into another in molecular and material systems, e.g. how plants absorb light, move electrons, and achieve efficient photosynthesis and overall energy capture. To that end, Subotnik will design new computational tools to study such energy flow-- seeking a complete microscopic description and focusing especially on spin degrees of freedom (noting that spin has usually been neglected or not treated properly in previous works). This project will connect very different scientific arenas, including especially the chemists who study how heat loss emerges from electronic systems (which is wasteful) and the physicists seeking to design new memory devices based on spin instead of electrons (which is sometimes called "spintronics"). At the same time, this research project will also seek to explain exciting new (but often not well understood) experimental methods that have emerged in recent years that use visible light to transform one set of molecules into another set of molecules, thus bypassing conventional and often inefficient high-temperature thermal approaches.<br/><br/><br/>Modern semiclassical theories of photochemistry have made outstanding progress as far as understanding how photoexcited molecules relax and transfer energy to nuclear vibrations, but these same simulations almost never maintain total angular momentum conservation and when modeling intersystem crossing (ISC), this failure becomes very problematic. After all, within a photochemical experiment, angular momentum can arise in at least four distinct flavors (photonic, nuclear, electronic orbital, electronic spin) and move between different subsystems. For instance, the most basic example is that when a spin degree of freedom explicitly changes its angular momentum, the nuclei, electrons, and possibly photons must necessarily compensate for such a change. Unfortunately, however, standard nonadiabatic algorithms cannot capture this effect, especially if one seeks a description beyond mean-field theory. With this urgent need in mind, Subotnik will (i) develop and implement a host of new nonadiabatic semiclassical approaches that do conserve angular momentum, including an angular-momentum conserving surface-hopping formalism, and then (ii) apply the resulting methods to realistic simulations of ISC, ascertaining exactly when the spin degrees of freedom are correlated with nuclear dynamics and/or chemical transformations. Subotnik will also host a conference designed to bring together scientists from both the chemistry and physics communities with diverse interests and backgrounds in spin-dependent nonadiabatic dynamics simulations so as to advance as rapidly as possible research at the crucial intersection of dynamics, spintronics, and electronic structure.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
