Light-Matter Response Functions in Quantum-Electrodynamical Density-Functional Theory: Modi cations of Spectra and of the Maxwell Equations

ACS Photonics (2019)

Light-Matter Response Functions in Quantum-Electrodynamical Density-Functional Theory: Modi cations of Spectra and of the Maxwell Equations

Johannes Flick,Davis M. Welakuh,Michael Ruggenthaler,Heiko Appel, Angel Rubio

We introduce linear-response theory for non-relativistic quantum-electrodynamics in the long wavelength limit, which allows us to treat correlated excited-state phenomena of matter-photon systems from first principles. By using quantum-electrodynamical density-functional theory we can reformulate the resulting fully coupled photon-matter response equations as a pseudo-eigenvalue problem. This provides a direct extension of the conventional matter-only response theory. Our approach can be solved numerically very efficiently and existing ab-initio density-functional response implementations can be easily extended to take the full photon-matter response into account. We highlight how the coupling between light and matter changes the usual response functions and introduces new types of response functions that measure the matter-photon subsystem responses. We show how correlating light and matter changes the Maxwell equations and highlight how the spectra of real systems are changed upon strongly coupling to the photon field. A key feature of treating the combined matter-photon response is that natural lifetimes of excitations become directly accessible from first principles and no artificial broadening of spectra is required anymore. By introducing a straightforward extension of the random-phase approximation for the coupled matter-photon problem, we are able to present the first ab-initio spectra for a real molecular system that is coupled to the quantized electromagnetic field.

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Doi
http://dx.doi.org/https://doi.org/10.1021/acsphotonics.9b00768
arxiv
http://arxiv.org/abs/1803.02519
Notes
We would like to thank Christian Schafer and Norah Hoffmann for insightful discussions, Sebastian Ohlmann for help with the implementation and acknowledge financial support from the European Research Council (ERC-2015-AdG-694097), by the European Union's H2020 programunder GA no.676580 (NOMAD).

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