Dynamical coupling of plasmons and molecular excitations by hybrid quantum/classical calculations: time-domain approach

• Published in: Journal of physics. Condensed matter 2014-08, Vol.26 (31), p.315013-315013
• Main Authors: Sakko, Arto, Rossi, Tuomas P, Nieminen, Risto M
• Format: Article
• Language: English
• Subjects: computational electrodynamics; density functional theory; metal-molecule interactions; multiscale methods; nanotechnology; plasmonics
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/0953-8984/26/28/315013

The presence of plasmonic material influences the optical properties of nearby molecules in untrivial ways due to the dynamical plasmon-molecule coupling. We combine quantum and classical calculation schemes to study this phenomenon in a hybrid system that consists of a Na2 molecule located in the gap between two Au/Ag nanoparticles. The molecule is treated quantum-mechanically with time-dependent density-functional theory, and the nanoparticles with quasistatic classical electrodynamics. The nanoparticle dimer has a plasmon resonance in the visible part of the electromagnetic spectrum, and the Na2 molecule has an electron-hole excitation in the same energy range. Due to the dynamical interaction of the two subsystems the plasmon and the molecular excitations couple, creating a hybridized molecular-plasmon excited state. This state has unique properties that yield e.g. enhanced photoabsorption compared to the freestanding Na2 molecule. The computational approach used enables decoupling of the mutual plasmon-molecule interaction, and our analysis verifies that it is not legitimate to neglect the backcoupling effect when describing the dynamical interaction between plasmonic material and nearby molecules. Time-resolved analysis shows nearly instantaneous formation of the coupled state, and provides an intuitive picture of the underlying physics.