title: Polaron dynamics with off-diagonal coupling: beyond the Ehrenfest approximation.
abstract: Treated traditionally by the Ehrenfest approximation, the dynamics of a one-dimensional molecular crystal model with off-diagonal exciton-phonon coupling is investigated in this work using the Dirac-Frenkel time-dependent variational principle with the multi-D2Ansatz. It is shown that the Ehrenfest method is equivalent to our variational method with the single D2Ansatz, and with the multi-D2Ansatz, the accuracy of our simulated dynamics is significantly enhanced in comparison with the semi-classical Ehrenfest dynamics. The multi-D2Ansatz is able to capture numerically accurate exciton momentum probability and help clarify the relation between the exciton momentum redistribution and the exciton energy relaxation. The results demonstrate that the exciton momentum distributions in the steady state are determined by a combination of the transfer integral and the off-diagonal coupling strength, independent of the excitonic initial conditions. We also probe the effect of the transfer integral and the off-diagonal coupling on exciton transport in both real and reciprocal space representations. Finally, the variational method with importance sampling is employed to investigate temperature effects on exciton transport using the multi-D2Ansatz, and it is demonstrated that the variational approach is valid in both low and high temperature regimes.
authors.affiliation: Division of Materials Science, Nanyang Technological University, Singapore, Singapore. yzhao@ntu.edu.sg.
authors.forename: Zhongkai
authors.initials: Z
authors.lastname: Huang
authors.affiliation: Division of Materials Science, Nanyang Technological University, Singapore, Singapore. yzhao@ntu.edu.sg and Department of Physics, Zhejiang University, Hangzhou 310027, China.
authors.forename: Lu
authors.initials: L
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China.
authors.forename: Changqin
authors.initials: C
authors.lastname: Wu
authors.affiliation: Division of Materials Science, Nanyang Technological University, Singapore, Singapore. yzhao@ntu.edu.sg.
authors.forename: Lipeng
authors.initials: L
authors.lastname: Chen
authors.affiliation: Institute for Theoretical Physics, Technische Universität Dresden, D-01062 Dresden, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Grossmann
authors.affiliation: Division of Materials Science, Nanyang Technological University, Singapore, Singapore. yzhao@ntu.edu.sg.
authors.forename: Yang
authors.initials: Y
authors.lastname: Zhao