title: Accounting for intra-molecular vibrational modes in open quantum system description of molecular systems.
abstract: Electronic-vibrational dynamics in molecular systems that interact with an environment involve a large number of degrees of freedom and are therefore often described by means of open quantum system approaches. A popular approach is to include only the electronic degrees of freedom into the system part and to couple these to a non-Markovian bath of harmonic vibrational modes that is characterized by a spectral density. Since this bath represents both intra-molecular and external vibrations, it is important to understand how to construct a spectral density that accounts for intra-molecular vibrational modes that couple further to other modes. Here, we address this problem by explicitly incorporating an intra-molecular vibrational mode together with the electronic degrees of freedom into the system part and using the Fano theory for a resonance coupled to a continuum to derive an "effective" bath spectral density, which describes the contribution of intra-molecular modes. We compare this effective model for the intra-molecular mode with the method of pseudomodes, a widely used approach in simulation of non-Markovian dynamics. We clarify the difference between these two approaches and demonstrate that the respective resulting dynamics and optical spectra can be very different.
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720, USA. roden@berkeley.edu
authors.forename: Jan
authors.initials: J
authors.lastname: Roden
authors.forename: Walter T
authors.initials: WT
authors.lastname: Strunz
authors.forename: K Birgitta
authors.initials: KB
authors.lastname: Whaley
authors.forename: Alexander
authors.initials: A
authors.lastname: Eisfeld
mesh_terms: D008954:Models, Biological; D011789:Quantum Theory; D013054:Spectrophotometry, Atomic; D014732:Vibration