Real-time time-dependent density functional theory, in conjunction with the Ehrenfest molecular dynamics scheme, is becoming a popular methodology to investigate ultrafast phenomena on the nanoscale. Thanks to recent developments, it is also possible to explicitly include in the simulations a time-dependent laser pulse, thereby accessing the transient excitation regime. However, the complexity entailed in these calculations calls for in-depth analysis of the accessible and yet approximate (either “dressed” or “bare”) quantities in order to evaluate their ability to provide us with a realistic picture of the simulated processes. In this work, we analyze the ultrafast dynamics of three small molecules (ethylene, benzene, and thiophene) excited by a resonant laser pulse in the framework of the adiabatic local-density approximation. The electronic response to the laser perturbation in terms of induced dipole moment and excited-state population is compared to the results given by an exactly solvable two-level model. In this way, we can interpret the charge-carrier dynamics in terms of simple estimators, such as the number of excited electrons. From the computed transient absorption spectra, we unravel the appearance of nonlinear effects such as excited-state absorption and vibronic coupling. In this way, we observe that the laser excitation affects the vibrational spectrum by enhancing the anharmonicities therein, while the coherent vibrational motion contributes to stabilizing the electronic excitation already within a few tens of femtoseconds.
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7 August 2020
Research Article|
August 03 2020
Understanding real-time time-dependent density-functional theory simulations of ultrafast laser-induced dynamics in organic molecules
Jannis Krumland;
Jannis Krumland
1
Humboldt-Universität zu Berlin, Physics Department and IRIS Adlershof
, 12489 Berlin, Germany
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Ana M. Valencia
;
Ana M. Valencia
1
Humboldt-Universität zu Berlin, Physics Department and IRIS Adlershof
, 12489 Berlin, Germany
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Stefano Pittalis
;
Stefano Pittalis
2
CNR - Istituto Nanoscienze
, 41125 Modena, Italy
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Carlo A. Rozzi
;
Carlo A. Rozzi
2
CNR - Istituto Nanoscienze
, 41125 Modena, Italy
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Caterina Cocchi
Caterina Cocchi
a)
1
Humboldt-Universität zu Berlin, Physics Department and IRIS Adlershof
, 12489 Berlin, Germany
3
Carl von Ossietzky Universität Oldenburg, Institute of Physics
, 26129 Oldenburg, Germany
a)Author to whom correspondence should be addressed: [email protected]
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a)Author to whom correspondence should be addressed: [email protected]
J. Chem. Phys. 153, 054106 (2020)
Article history
Received:
March 19 2020
Accepted:
July 10 2020
Citation
Jannis Krumland, Ana M. Valencia, Stefano Pittalis, Carlo A. Rozzi, Caterina Cocchi; Understanding real-time time-dependent density-functional theory simulations of ultrafast laser-induced dynamics in organic molecules. J. Chem. Phys. 7 August 2020; 153 (5): 054106. https://doi.org/10.1063/5.0008194
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