The interplay between electron and energy transfer in molecular nanosystems

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Abraham Nitzan of the University of Pennsylvania is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry. They are supported to develop a conceptual framework and computational methodologies to address energy conversion processes on the nano scale. Energy conversion - the change from one form of available energy to another, has always been an important subject for fundamental research as well as technological applications. Scientists and engineers strive to increase the efficiency of converting energy to useful forms on one hand, and to limit its escape as wasted forms on the other. As science and technology enter the nano age, such problems re-emerge in new forms that require new conceptual frameworks and new experimental and computational approaches for their description. Nitzan and his coworkers focus on several central issues within this effort: The description of heat transfer on the molecular scale and the coupling between charge and heat transport in molecular systems. They are constructing a quantum thermodynamics framework to address such processes, their inter-relationships and their efficiencies. The research impacts a diverse range of applications of nanoscience -- from dissipation and information loss in quantum computing to the efficiency of operation of nano-photo-devices as well as biological electron-transfer processes. The Nitzan group provides research opportunities for students at all levels: high school, undergraduate, graduate and postdoctoral. This project addresses three major problems: 1) electron transfer across thermal gradients. Although coupling between electron and energy transfer in metals is known to exist, it is usually disregarded in models of electron hopping in molecular systems and often overlooked even in semiconductors. The objective is to study the interplay between electron and heat transport in such systems, to propose ways for their experimental observation, and to examine their implications for nanoscale energy conversion devices. 2) heat transfer on the molecular scale, where the connection between structural and dynamical properties of molecules and their ability to conduct, utilize and dissipate heat is being examined. Here the proposed investigation contacts the growing number of experimental groups working in this area as well as with other computational investigations. 3) Finally, this project continues work in the Nitzan group aimed at developing a general framework for the description of such process within a quantum generalization of thermodynamics of small systems. This work aims to achieve the equivalent of what classical thermodynamics does on the macroscopic scale: to provide concepts, theoretical structure and computational methodologies for addressing processes underlying energy conversion, dissipation and utilization that occur on the molecular scale where quantum mechanics is strongly manifested. The processes studied in the first two parts of the project will be formulated in this language as special cases of what should become a quantum thermodynamics theory of nanoscale systems that strongly interact with their environment.