Understanding plasmon coupling in nanoparticle dimers using molecular orbitals and configuration interaction

Area of Science:

• Theoretical physics
• Materials science
• Nanotechnology

Background:

• Understanding plasmonic properties of atomic nanostructures is crucial for nanoscale device applications.
• The electronic structure and optical responses of nanodimers are complex and depend on interatomic distances and electronic interactions.

Purpose of the Study:

• To theoretically investigate the electronic structure and optical properties of atomic nanowire and nanorod dimers.
• To analyze the origin and behavior of plasmon modes, specifically bonding dipole plasmon (BDP) and charge-transfer plasmon (CTP) modes, in these nanostructures.

Main Methods:

• Density Functional Theory (DFT) for electronic structure calculations.
• Time-Dependent Density Functional Theory (TDDFT) for optical property simulations.
• Configuration Interaction (CI) analysis to understand transition couplings.

Main Results:

• At separation distances > 0.75 nm, a single BDP mode is observed, arising from constructive coupling of transitions.
• At shorter distances, wave-function overlap leads to both constructive and destructive coupling, resulting in multiple spectral features.
• A CTP mode emerges from destructive coupling, while the BDP mode arises from constructive coupling of the same transitions.
• The splitting between CTP and BDP modes is sensitive to the amount of exact Hartree-Fock exchange (HFX) in the functional.

Conclusions:

• The interplay of constructive and destructive couplings dictates plasmonic behavior in atomic nanodimers.
• Significant HFX (≥50%) causes CTP and BDP modes to merge, highlighting the importance of exact exchange in predicting CTP modes in plasmonic systems.