Non-Markovian quantum state diffusion for absorption spectra of molecular aggregates

TL;DR

This paper compares the non-Markovian quantum state diffusion approach with the pseudomode method for calculating absorption spectra in molecular aggregates, demonstrating good agreement and discussing their respective advantages and limitations.

Contribution

It validates the NMQSD approximation by comparing it with exact pseudomode results for complex molecular systems.

Findings

NMQSD results mostly agree with pseudomode calculations.

The pseudomode method can determine exact spectra for small aggregates.

The paper discusses the advantages and disadvantages of both approaches.

Abstract

In many molecular systems one encounters the situation where electronic excitations couple to a quasi-continuum of phonon modes. That continuum may be highly structured e.g. due to some weakly damped high frequency modes. To handle such a situation, an approach combining the non-Markovian quantum state diffusion (NMQSD) description of open quantum systems with an efficient but abstract approximation was recently applied to calculate energy transfer and absorption spectra of molecular aggregates [Roden, Eisfeld, Wolff, Strunz, PRL 103 (2009) 058301]. To explore the validity of the used approximation for such complicated systems, in the present work we compare the calculated (approximative) absorption spectra with exact results. These are obtained from the method of pseudomodes, which we show to be capable of determining the exact spectra for small aggregates and a few pseudomodes. It turns out that in the cases considered, the results of the two approaches mostly agree quite well. The advantages and disadvantages of the two approaches are discussed.