Session X03: Challenges for excited states and dynamics III

A QM/MM study of photoisomerization in artificial molecular switches

This abstract not available.   

Effect of Raman Process on the Nonadiabatic Dynamics of Electron-Phonon-Photon systems

We studied the wavepacket dynamics of coupled electron-phonon-photon systems by numerical calculations on the time-dependent Schrodinger equation. We take into account multiple photon modes in order to discuss the effect of Raman process. It has been shown that the conical intersection which appears on the potential energy surfaces plays an important role in photoexcitation/deexcitation dynamics. We consider that the wavelength of the photons is converted by the Raman process, and that it should be taken into account when both photons and phonons are coulpled with electrons. In the present paper, we discuss the effect of Raman process on the wavepacket motion by calculating the excited-state population, the wavepacket trajectories, and the entanglement entropy.   

High-Dimensional Quantum Dynamics of Functional Organic Polymer Materials: Coherence, Confinement, and Disorder

This talk addresses quantum dynamical studies of ultrafast photo-induced exciton migration and dissociation in functional organic materials, in view of understanding the intricate interplay of electronic delocalization, coherent nonadiabatic dynamics, and trapping phenomena. Our approach combines first-principles parametrized Hamiltonians, based on TDDFT and/or high-level electronic structure calculations, with accurate quantum dynamics simulations using the Multi-Configuration Time-Dependent Hartree (MCTDH) method [1] and its hierarchical multi-layer (ML-MCTDH) variant [2]. The talk will specifically focus on (i) exciton dissociation and free carrier generation in regioregular donor-acceptor assemblies [3-5], (ii) exciton multiplication in acene materials [6] and (iii) the elementary mechanism of exciton migration and creation of charge-transfer excitons in polythiophene and poly-(p-phenylene vinylene) type materials [7]. Special emphasis is placed on the influence of structural (dis)order and molecular packing, which can act as a determining factor in transfer efficiencies. Against this background, we will comment on the role of temporal and spatial coherence along with a consistent description of the transition to a classical-statistical regime.

[1] G. A. Worth, H.-D. Meyer, H. Köppel, L. S. Cederbaum, and I. Burghardt, Int. Rev. Phys. Chem. 27, 569 (2008).
[2] H. Wang, J. Phys. Chem. A 119, 7951 (2015).
[3] M. Polkehn, H. Tamura, P. Eisenbrandt, S. Haacke, S. Méry, and I. Burghardt, J. Phys. Chem. Lett. 7, 1327 (2016).
[4] M. Polkehn, P. Eisenbrandt, H. Tamura, and I. Burghardt, Int. J. Quantum Chem. 2017, https://doi.org/10.1002/qua.25502.
[5] M. Polkehn, H. Tamura, and I. Burghardt, J. Phys. B: At. Mol. Opt. Phys. 2017, https://doi.org/10.1088/1361-6455/aa93d0.
[6] H. Tamura, M. Huix-Rotllant, I. Burghardt, Y. Olivier, and D. Beljonne, Phys. Rev. Lett. 115, 107401 (2015).
[7] R. Binder, M. Polkehn, T. Ma, and I. Burghardt, Chem. Phys. 482, 16 (2017).   

Path-Integral Isomorphic Hamiltonian for Including Nuclear Quantum Effects in Non-adiabatic Dynamics

We describe a path-integral approach for including nuclear quantum effects in non-adiabatic chemical dynamics simulations. For a general physical system with multiple electronic energy levels, a corresponding isomorphic Hamiltonian is introduced, such that Boltzmann sampling of the isomorphic Hamiltonian with classical nuclear degrees of freedom yields the exact quantum Boltzmann distribution for the original physical system. In the limit of a single electronic energy level, the isomorphic Hamiltonian reduces to the familiar cases of either ring polymer molecular dynamics (RPMD) or centroid molecular dynamics Hamiltonians, depending on implementation. An advantage of the isomorphic Hamiltonian is that it can easily be combined with existing mixed quantum-classical dynamics methods, such as surface hopping or Ehrenfest dynamics, to enable the simulation of electronically non-adiabatic processes with nuclear quantum effects. We present numerical applications of the isomorphic Hamiltonian to model two- and three-level systems, with encouraging results that include improvement upon a previously reported combination of RPMD with surface hopping in the deep-tunneling regime.   

Excited State Variational Principles for Real Solids

We will present recent progress on the adaptation for solid state applications of variational Monte Carlo methods that optimize wave functions directly for excited states. These methods are based on rigorous variational principles that allow an interior eigenstate of the Hamiltonian to be targeted directly based on its location in the spectrum in direct analogue to how the traditional variational principle targets the ground state. In combination with recent progress in Monte Carlo wave function optimization techniques, such methods offer a new opportunity in modeling the optical band gaps of real materials. In particular, the systematic improvability and non-perturbative nature of the approach makes it especially appealing in the context of strongly correlated materials, for which current many-body methods face substantial difficulties.   

Ultrafast PEPICO Spectroscopy of Electron Correlation Effects and Nonadiabatic Population Transfer Between HOMO-Excited and HOMO-1-Excited States in Acetone and Methyl Azide

We employ ultrafast pump-probe spectroscopy with photoelectron-photoion coincidence (PEPICO) detection to observe the complex dynamics of highly excited states of acetone and methyl azide. Both molecules are excited by an 8.0 eV photon to a mixed character Rydberg-valence excited state, then probed with 1.6, 3.2, or 4.8 eV photons to ionize from the excited state. Methyl azide shows 25 fs population transfer from a strongly mixed-character state to a pure valence state, and ab-initio multiple spawning (AIMS) calculations reveal that the transfer is driven by strong nonadiabatic coupling through a conical intersection seam well above the minimum energy conical intersection. Acetone exhibits a very fast decay to a state with mixed Rydberg-valence character. This state then decays in 330 fs predominantly by internal conversion to a pure 3s Rydberg state.   

Linear and nonlinear spectroscopy in the condensed phase

I will describe the use of wavefunction-based techniques in order to calculate the linear and nonlinear optical response of condensed phase materials, including three-dimensional solids and low-dimensional nanostructures. In particular, I will discuss approaches based on equation-of-motion coupled-cluster theory, as well as its relation to the GW approximation for charged excitations and the Bethe-Salpeter equation for neutral excitations.