Heat Transport in a Spin-Boson Model at Low Temperatures: A Multilayer Multiconfiguration Time-Dependent Hartree Study

Extending our previous work, quantum dynamic simulations are performed to study low temperature heat transport in a spin-boson model where a two-level subsystem is coupled to two independent harmonic baths. Multilayer multiconfiguration time-dependent Hartree theory is used to numerically evaluate the thermal flux, for which the bath is represented by hundreds to thousands of modes. The simulation results are compared with the approximate Redfield theory approach, and the physics is analyzed versus different physical parameters.

Absorption and Circular Dichroism Spectra of Molecular Aggregates with the Full Cumulant Expansion.

The exciton Hamiltonian of multichromophoric aggregates can be probed by spectroscopic techniques such as linear absorption and circular dichroism. In order to compare calculated Hamiltonians to experiments, a lineshape theory is needed, which takes into account the coupling of the excitons with inter- and intramolecular vibrations. This coupling is normally introduced in a perturbative way through the cumulant expansion formalism, and further approximated by assuming a Markovian exciton dynamics, for example with the modified Redfield theory.<br><br>Here we present an implementation of the full cumulant expansion (FCE) formalism [Ma and Cao, <i>J. Chem. Phys.</i> <b>2015</b>, 142, 094106 ] to efficiently compute absorption and circular dichroism spectra of molecular aggregates beyond the Markov approximation, without restrictions on the form of the exciton-phonon coupling. By employing the LH2 system of purple bacteria as a challenging test case, we compare the FCE lineshapes with the Markovian lineshapes obtained with the modified Redfield theory, showing that the latter present a much poorer agreement with experiments. The FCE approach instead accurately describes the lineshapes, especially in the vibronic sideband of the B800 peak. We envision that the FCE approach will become a valuable tool for accurately comparing model exciton Hamiltonians with optical spectroscopy experiments.

Absorption and Circular Dichroism Spectra of Molecular Aggregates with the Full Cumulant Expansion.

The exciton Hamiltonian of multichromophoric aggregates can be probed by spectroscopic techniques such as linear absorption and circular dichroism. In order to compare calculated Hamiltonians to experiments, a lineshape theory is needed, which takes into account the coupling of the excitons with inter- and intramolecular vibrations. This coupling is normally introduced in a perturbative way through the cumulant expansion formalism, and further approximated by assuming a Markovian exciton dynamics, for example with the modified Redfield theory.<br><br>Here we present an implementation of the full cumulant expansion (FCE) formalism [Ma and Cao, <i>J. Chem. Phys.</i> <b>2015</b>, 142, 094106 ] to efficiently compute absorption and circular dichroism spectra of molecular aggregates beyond the Markov approximation, without restrictions on the form of the exciton-phonon coupling. By employing the LH2 system of purple bacteria as a challenging test case, we compare the FCE lineshapes with the Markovian lineshapes obtained with the modified Redfield theory, showing that the latter present a much poorer agreement with experiments. The FCE approach instead accurately describes the lineshapes, especially in the vibronic sideband of the B800 peak. We envision that the FCE approach will become a valuable tool for accurately comparing model exciton Hamiltonians with optical spectroscopy experiments.

Simulating exciton migration and annihilation dynamics in higher order spectroscopies of a molecular trimer

We present simulations of 3rd and 5th order multidimensional time-dependent signals of a molecular trimer. The developed model allows for the simulation of both signal types within one theoretical framework. We therefore extended standard Redfield theory of exciton migration by a new term to include the process of exciton-exciton annihilation.

Conductance and activation energy for electron transport in series and parallel intramolecular circuits

We investigate electron transport through series and parallel intramolecular circuits in the framework of the multi-level Redfield theory.