Radiative emission in quantum dynamics simulations

DAMIAN A SCHERLIS

Vancouver

Congreso; 12th Congress of the World Association of Theoretical and Computational Chemists; 2022

World Association of Theoretical and Computational Chemists

Quantumdynamics simulations provide the evolution of the charge density as afunction of time. In recent years, the application of these methodsto chemical systems has contributed important insights on electronicexcitations, spectroscopy, photochemistry and transport. Even so,this kind of simulations typically lack an important ingredient:radiative dissipation. The representation of spontaneous emission, orthe radiative decay of an excited electronic state, is absent fromcurrent approaches, which means that the energy absorbed during theexcitation of a molecule at zero temperature will remain in thesystem in the form of undamped dipole oscillations, indefinitely intime, which is unphysical. Inthis talk, we introduce a Langrangian formulation based on the ideathat the electromagnetic radiation of the charge density can beapproximated as the power dissipated by a classical dipole. Thisstrategy allows us to derive a semiclassical equation of motion thatincorporates radiative dissipation in a simple way, leading to afirst-principles formalism that quantitatively captures decay rates,natural broadening, and absorption intensities. Its implementation inreal time TDDFT simulations produces accurate excitation lifetimesfor atomic species, with errors comparable to or below thoseresulting from highly correlated quantum chemistry methods, and atsignificantly lower computational costs. This formalism thus bringswithin reach the ab-initio modeling of a diversity of photophysicalprocesses, from resonance energy transfer to time-resolvedspectroscopy and photoluminescence. Inparticular, we illustrate its application to the description ofcooperative emission phenomena known as superradiance andsubradiance. In the first case the coherent radiation of multipleemitters boosts the radiated power and shortens the excitationlifetime. For these reasons superradiance has attracted a lot ofinterest for high-speed light-emitting devices, lasers, or fastoptical interconnects. On the other hand, in subrradiance theradiative decay is halted thanks to the cancellation of theindividual dipoles, allowing for the indefinite prolongation of anexcited state. This is envisioned as a way to store optical energy.Along this talk both phenomena are explored in molecular systems inthe context of TDDFT simulations in real time.p { margin-bottom: 0.1in; direction: ltr; color: #000000; line-height: 115%; orphans: 2; widows: 2 }p.western { font-family: "Liberation Serif", "Times New Roman", serif; font-size: 12pt; so-language: en-US }p.cjk { font-family: "Noto Sans CJK SC"; font-size: 12pt; so-language: zh-CN }p.ctl { font-family: "Lohit Devanagari"; font-size: 12pt; so-language: hi-IN }