Modeling molecular J and H aggregates using multiple-Davydov D2 ansatz

The linear absorption spectrum of J and H molecular aggregates is studied using the time-dependent Dirac-Frenkel variational principle (TDVP) with the multi-Davydov D-2 (mD(2)) trial wavefunction (Ansatz). Both the electronic and vibrational molecular degrees of freedom (DOF) are considered. By inspecting and comparing the absorption spectrum of both open and closed chain aggregates over a range of electrostatic nearest neighbor coupling and temperature values, we find that the mD(2) Ansatz is necessary for obtaining an accurate aggregate absorption spectrum in all parameter regimes considered, while the regular Davydov D-2 Ansatz is not sufficient. Establishing a relationship between the model parameters and the depth of the mD(2) Ansatz is the main focus of this study. Molecular aggregate wavepacket dynamics, during excitation by an external field, is also studied. We find the wavepacket to exhibit an out-of-phase oscillatory behavior along the coordinate and momentum axes and an overall wavepacket broadening, implying the electron-vibrational (vibronic) eigenstates of an aggregate to reside on non-parabolic energy surfaces.

Automated summary

This study investigates the linear absorption spectrum of J and H molecular aggregates using the time-dependent Dirac-Frenkel variational principle with the multi-Davydov D-2 trial wavefunction. Both the electronic and vibrational degrees of freedom are considered. The study finds that the mD(2) Ansatz is necessary for accurately predicting the absorption spectrum in all parameter regimes, while the regular Davydov D-2 Ansatz is insufficient. The study also explores the wavepacket dynamics during excitation and finds that the electron-vibrational eigenstates of the aggregate reside on non-parabolic energy surfaces.