Density Functional Tight-Binding Captures Plasmon-Driven H$_2$ Dissociation on Al Nanocrystals

TL;DR

This study uses density functional tight-binding to explore how aluminum nanocrystals interact with light and facilitate hydrogen dissociation, revealing size and shape effects on plasmon resonances and reaction efficiency.

Contribution

It demonstrates DFTB's effectiveness in modeling plasmonic and catalytic processes in aluminum nanocrystals at realistic sizes and timescales, providing mechanistic insights.

Findings

Al nanocrystals exhibit size-dependent UV plasmon resonances.

Hot electrons can dissociate H2 molecules within tens of femtoseconds.

Dipolar plasmon modes are more efficient than interband transitions for catalysis.

Abstract

Aluminum nanocrystals offer a promising platform for plasmonic photocatalysis, yet a detailed understanding of their electron dynamics and consequent photocatalytic performance has been challenging thus far due to computational limitations. Here, we employ density functional tight-binding methods (DFTB) to investigate the optical properties and H₂ dissociation dynamics of Al nanocrystals with varying sizes and geometries. Our real-time simulations reveal that Al's unique free-electron nature enables efficient light-matter interactions and rapid electronic thermalization. Cubic and octahedral nanocrystals ranging from 0.5 to 4.5 nm exhibit size-dependent plasmon resonances in the UV, with distinct spectral features arising from the particle geometry and electronic structure. By simulating H₂ dissociation near Al nanocrystals, we demonstrate that hot electrons generated through plasmon excitation can overcome the molecule's strong chemical bond within tens of femtoseconds. The laser intensity threshold is comparable to previous reports for Ag nanocrystals, though significantly lower than that of Au. Notably, the dipolar plasmon mode demonstrates higher efficiency for this reaction than the localized interband transition for particles at these sizes. Taken together, this work provides mechanistic insights into plasmon-driven catalysis and showcases DFTB's capability to study quantum plasmonics at unprecedented length and time scales.