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arXiv · 1908.10130

Quantum dissipative systems beyond the standard harmonic model: features of linear absorption and dynamics

Luke D. Smith·Arend G. Dijkstra
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Abstract

Current simulations of ultraviolet-visible absorption lineshapes, and dynamics of condensed phase systems, largely adopt a harmonic description to model vibrations. Often, this involves a model of displaced harmonic oscillators that have the same curvature. Although convenient, for many realistic molecular systems this approximation no longer suffices. We elucidate non-standard harmonic, and anharmonic effects, on linear absorption and dynamics using a stochastic Schr\"{o}dinger equation approach to account for the environment. Firstly, a harmonic oscillator model with ground and excited potentials that differ in curvature is utilised. Using this model, it is shown that curvature difference gives rise to an additional sub-structure in the vibronic progression of absorption spectra. This effect is explained, and subsequently quantified, via a derived expression for the Franck-Condon coefficients. Subsequently, anharmonic features in dissipative systems are studied, using a Morse potential, and parameters that correspond to the diatomic molecule $H_{2}$ for differing displacements and environment interaction. Lastly using a model potential, the population dynamics and absorption spectra for the stiff-stilbene photoswitch is presented and features are explained by a combination of curvature difference and anharmonicity in the form of potential energy barriers on the excited potential.

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Luke D. Smith, Arend G. Dijkstra. 2019-08-27. Quantum dissipative systems beyond the standard harmonic model: features of linear absorption and dynamics. https://doi.org/10.1063/1.5122896

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