Nanostructures have tremendous potentials to be used for energy and fuel productions, either in photovoltaic  or solar photocatalysis for water splitting.  To design and control these applications, we need to understand the transports of the photon generated carriers in these systems. One challenge to simulate these systems using ab initio method is the large system size, e.g., one nanocrystal might contain tens of thousands of atoms.  Recently, we have developed several approaches to study the carrier transport in these systems. The first approach uses analytical formulas like the Marcus theory [1]. The electronic structures of the nanosystem are calculated using a charge patching method [2], while the electronic coupling between the localized states is calculated by their energy anticrossing [3,4]. GW corrections are used to correct the errors in the density functional theory (DFT) eigen energies [5].  We obtained quantitative agreement with the experiments for the charge transfer rates. In the second approach, nonadiabatic molecular dynamics is used to simulate the carrier transport directly [6]. In such simulations, the electron wave function follows the time dependent Schrodinger's equation while the atomic nuclear follow the classical Newton's law.  One challenge in the time dependent Schrodinger's equation simulation is the requirement for small time step (attosecond). We have developed an algorithm which increases the time step to fs for the most time consuming part of the calculation [6]. We have used this approach to simulate a monolayer of organic molecules forming a Herringbone pattern. The system contains 7,000 atoms, and 1ps  simulation is carried out to reveal the hole dynamics.  Charge patching method is used to construct the DFT Hamiltonian of the system without direct selfconsistent field calculations. We found that the thermodynamic disorder induces wave function localization, while the energy crossing between neighboring states contributes to the hole mobility.Acknowledgment: This work was supported by the Director, Office of Science (SC), Basic Energy Science (BES)/Materials Science and Engineering Division (MSED) of the U.S. Department of Energy (DOE)  through the Condensed Matter Theory program at Lawrence Berkeley National Laboratory under Contract DE-AC02-05CH11231.[1] R. A. Marcus, Annu. Rev. Phys. Chem. 15, 155 (1964).[2] J. Li, L.W. Wang, Phys. Rev. B 72, 125325 (2005).[3]  I-H. Chu, M. Radulaski, N. Vukmirovic, H.-P. Cheng, L.W. Wang, J. Phys. Chem. C 115, 21409 (2011).[4]  I.-H. Chen, J. Trinastic, L.W. Wang, H.P. Cheng, Phys. Rev. B 89, 115415 (2014).[5] K. Tarafder, Y. Surendranath, J.H. Olshansky, A.P. Alivisatos, L.W. Wang, J. Amer. Chem. Soc. (10.1021/ja500936n)[6] J. Ren, N. Vukmirovic, L.W. Wang,  Phys. Rev. B 87, 205117 (2013)

Ab initio calculations of charge transports in nanosystems

248th National Meeting (2014)

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