Nanoscale Simulations

Electron transfer

Fig 3: Electron transfer in a solar cell, at the interface between a solid/liquid
Fig 3: Electron transfer in a solar cell, at the interface between a solid/liquid.[45,44]

Electron transfer (ET) has been the driving force for much of my recent work[23,24,25,26,27,31,38,44,45]. This is a particularly interesting topic for advanced methods in AIMD, because it unavoidably involves electrons, chemical reactions, long range interactions, and a finite temperature. At the same time, it is particularly challenging in various ways. So far, we have tackled to problem by determination of free energy differences (redox potential differences), and solvent reorganization energies for small molecules in solution using QM[23] and MM[24] sampling and for proteins using MM sampling with the full system, or the active site described using DFT[26]. We have been able to show that good accuracy can be obtained for redox potential differences[23,26], and that subtle solvent effects, beyond the continuum approximation, can be captured[24,26] for both the redox potential and the solvent reorganization energy. The matrix element describing the quantum coupling between donor and acceptor has so far been proven difficult to obtain correctly using DFT. We have made good progress[31,44,45] on models of dye sensitized solar cells (DSSC). In this work, we embrace the complexity of the system, and take all components of the interface explicitly into account (see Fig. 3). So far, we have characterized the binding geometry of the dye on the surface, the solvent at the interface, the properties of the electrolyte, and the dye regeneration process. Pioneering simulations of the actual electron injection process (using in model shown in Fig. 3, with density functionals including Hartree-Fock exchange and based on Ehrenfest MD) are in progress. These truly demanding calculations, running on 8192 XT5 cores for a least one week, introduce the electronic timescale (atto-seconds) to simulations of nanometer-sized structures.


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