Plasmons in molecules: microscopic characterization based on orbital transitions and momentum conservation

Area of Science:

• Solid state physics
• Quantum chemistry
• Materials science

Background:

• Electronic excitations in solids are classified as plasmons (collective electron density oscillations) or single-particle excitations.
• The random-phase approximation (RPA) describes plasmons microscopically as particle-hole transitions.
• Small systems like molecules and nanoclusters lack properties for solid-state plasmon formation, leading to an ambiguous microscopic definition.

Purpose of the Study:

• To analyze the microscopic properties of molecular plasmons.
• To compare molecular plasmons with the homogeneous electron gas (HEG) as a model system.
• To validate derived characteristics by analyzing electronic excitation vectors in linear polyenes.

Main Methods:

• Microscopic analysis of molecular plasmons.
• Comparison with the homogeneous electron gas model.
• Application of the second-order algebraic diagrammatic construction (ADC(2)) scheme for the polarization propagator.

Main Results:

• Identified key microscopic differences and similarities between molecular plasmons and HEG plasmons.
• Established a theoretical framework for characterizing molecular plasmons.
• Validated the theoretical approach using linear polyene systems.

Conclusions:

• Provided a clearer microscopic definition for molecular plasmons.
• Demonstrated the utility of the ADC(2) scheme for studying molecular plasmons.
• Advanced the understanding of electronic excitations in small systems for plasmonics applications.