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FOB-SH: Fragment orbital-based surface hopping for charge carrier transport in organic and biological molecules and materials

Spencer, J; Gajdos, F; Blumberger, J; (2016) FOB-SH: Fragment orbital-based surface hopping for charge carrier transport in organic and biological molecules and materials. Journal of Chemical Physics , 145 (6) 10.1063/1.4960144. Green open access

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Abstract

We introduce a fragment orbital-based fewest switches surface hopping method, FOB-SH, designed to efficiently simulate charge carrier transport in strongly fluctuating condensed phase systems such as organic semiconductors and biomolecules. The charge carrier wavefunction is expanded and the electronic Hamiltonian constructed in a set of singly occupied molecular orbitals of the molecular sites that mediate the charge transfer. Diagonal elements of the electronic Hamiltonian (site energies) are obtained from a force field, whereas the off-diagonal or electronic coupling matrix elements are obtained using our recently developed analytic overlap method. We derive a general expression for the exact forces on the adiabatic ground and excited electronic state surfaces from the nuclear gradients of the charge localized electronic states. Applications to electron hole transfer in a model ethylene dimer and through a chain of ten model ethylenes validate our implementation and demonstrate its computational efficiency. On the larger system, we calculate the qualitative behaviour of charge mobility with change in temperature T for different regimes of the intermolecular electronic coupling. For small couplings, FOB-SH predicts a crossover from a thermally activated regime at low temperatures to a band-like transport regime at higher temperatures. For higher electronic couplings, the thermally activated regime disappears and the mobility decreases according to a power law. This is interpreted by a gradual loss in probability for resonance between the sites as the temperature increases. The polaron hopping model solved for the same system gives a qualitatively different result and underestimates the mobility decay at higher temperatures. Taken together, the FOB-SH methodology introduced here shows promise for a realistic investigation of charge carrier transport in complex organic, aqueous, and biological systems.

Type: Article
Title: FOB-SH: Fragment orbital-based surface hopping for charge carrier transport in organic and biological molecules and materials
Open access status: An open access version is available from UCL Discovery
DOI: 10.1063/1.4960144
Publisher version: http://doi.org/10.1063/1.4960144
Language: English
Additional information: The following article appeared in Spencer, J; Gajdos, F; Blumberger, J; (2016) FOB-SH: Fragment orbital-based surface hopping for charge carrier transport in organic and biological molecules and materials. Journal of Chemical Physics , 145 (6) 10.1063/1.4960144, and may be found at: http://doi.org/10.1063/1.4960144. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing.
Keywords: Science & Technology, Physical Sciences, Chemistry, Physical, Physics, Atomic, Molecular & Chemical, Chemistry, Physics, ELECTRON-TRANSFER REACTIONS, DENSITY-FUNCTIONAL THEORY, NONADIABATIC DYNAMICS, SEMIEMPIRICAL METHODS, EXCITON DISSOCIATION, SYSTEMS APPLICATION, SIMULATION, SEMICONDUCTORS, COUPLINGS, MODELS
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI: https://discovery.ucl.ac.uk/id/eprint/1516956
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