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Nonadiabatic Dynamics of Cycloparaphenylenes with TD-DFTB Surface Hopping

Abstract : We implemented a version of the decoherence-corrected fewest switches surface hopping based on linear-response time-dependent density functional tight binding (TD-DFTB), enhanced by transition density analysis. The method has been tested for the gas-phase relaxation dynamics of two cycloparaphenylene molecules, [8]CPP and [10]CPP, explaining some important features of their nonadiabatic dynamics, such as the origin of their long fluorescence lifetimes (related to the slow radiative emission from the S-1 state) and the trend of increasing the fluorescence rate with the molecular size (related to an increase in the S-1-S-0 energy gaps and oscillator strengths in the larger molecule). The quality of the TD-DFTB electronic structure information was assessed through four quantities: excitation energies; charge-transfer (CT) numbers, which estimate the charge transfer character of states; participation ratio (PR), which describes delocalization of electronic density; and participation ratio of natural transition orbitals (PRNTO), which describes the multiconfigurational character of states. These quantities were computed during dynamics and recomputed for the same geometries with the higher-level long-range-corrected TD-LC-DFTB and a lower-level single-determinant approximation for the excited states, SD-(LC)-DFTB. Taking TD-LC-DFTB as the standard, TD-DFTB underestimates the excitation energies by similar to 0.5 eV and overestimates CT and PR. SD-DFTB underestimates excitation energies and overestimates CT to the same extent that TD-DFTB does, but it predicts reasonable PR distributions. SD-LC-DFTB leads to an extreme overestimation of the excitation energies by similar to 3 eV, overestimates the charge transfer character of the state, but predicts the PR values very close to those obtained with TD-LC-DFTB.
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https://hal-amu.archives-ouvertes.fr/hal-01774209
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Submitted on : Monday, April 23, 2018 - 2:42:40 PM
Last modification on : Friday, October 16, 2020 - 3:35:33 AM

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Ljiljana Stojanovic, Saadullah G. Aziz, Rifaat H. Hilal, Felix Plasser, Thomas A. Niehaus, et al.. Nonadiabatic Dynamics of Cycloparaphenylenes with TD-DFTB Surface Hopping. Journal of Chemical Theory and Computation, American Chemical Society, 2017, 13 (12), pp.5846--5860. ⟨10.1021/acs.jctc.7b01000⟩. ⟨hal-01774209⟩

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