Charge Transfer via Electronic Coupling

Charge transfer processes are ubiquitous across chemistry, but they are computationally intensive to simulate. We are developing approaches to efficiently and accurately simulate  charge transfer using diabatic electronic couplings.

From cellular respiration and photosynthesis to the design of molecular devices and electrocatalysts, understanding and controlling charge transfer is important across a wide range of chemical disciplines. In recent years, simulations of charge transfer have become commonplace in determining the mechanism for a given process or finding what structural parameters can be tuned in order to direct and enhance current flow. Simulation can offer insights that are not readily obtainable from experiment, providing a molecular level view of a process and the means to study as yet unsynthesized compounds. A key challenge in this area is that most systems of practical interest (e.g. proteins, amorphous clusters, nanoscale devices) are too large to simulate fully quantum mechanically. We aim to address this problem by developing more computationally efficient methods to model charge transfer.

Fundamentally, charge transfer, either through-space or through-bonds, directs charge carriers from a donor to an acceptor. To model these processes, most approaches require expensive excited state calculations and multiple subcalculations of the donor and acceptor fragments individually. We have devised an algorithm to determine electronic couplings, which are directly related to charge transfer rates, from a single ground state DFT calculation. These same issues are exacerbated in simulations of solids, where the size of the systems require periodic boundary conditions (PBCs) to be used. More efficient methods would greatly aid efforts to optimize the performance of nanodevices bound to electrodes. We are currently working to extend our DFT coupling algorithm to use PBCs for cases where the donor and acceptor are chemically bound. 

A. Biancardi, M. Caricato*, A Benchmark Study of Electronic Couplings in Donor–Bridge–Acceptor Systems with the FMR-B Method; J. Chem. Theory Comput., 14, (2018) 2007.

A. Biancardi, S. C. Martin, C. Liss, M. Caricato*, Electronic Coupling for Donor-Bridge-Acceptor Systems with a Bridge-Overlap Approach; J. Chem. Theory Comput., 13, (2017) 4154.

A. Biancardi, C. Caraiani, W.-L. Chan, M. Caricato*, How the Number of Layers and Relative Position Modulate the Interlayer Electron Transfer in π-Stacked 2D Materials; J. Phys. Chem. Lett., 8, (2017) 1365. 

A. Biancardi, M. Caricato*, Evaluation of Electronic Coupling in Solids from Ab Initio Periodic Boundary Condition Calculations: The Case of Pentacene Crystal and Bilayer Graphene; J. Phys. Chem. C, 120, (2016) 17939.