Atomistic QM/Classical Modeling Accurately Calculates Surface-Enhanced Infrared Absorption Spectra of Adsorbed Molecules

Surface-enhanced infrared absorption (SEIRA) holds immense promise for identifying molecules at extremely low concentrations, but accurately modelling this phenomenon presents a significant challenge. Sveva Sodomaco, Piero Lafiosca, and Tommaso Giovannini, alongside their colleagues, address this by developing a new multiscale modelling approach that combines quantum mechanical calculations for molecules with classical descriptions of the metallic nanostructures that enhance the infrared signal. This method, which incorporates detailed atomic-level modelling of the metal, achieves accuracy comparable to more computationally demanding techniques, while remaining efficient enough to study complex systems. By applying this framework to adenine molecules adsorbed on gold nanoparticles and graphene, the researchers demonstrate a reliable way to predict vibrational responses in these hybrid plasmon-molecule systems, paving the way for improved sensor design and molecular analysis.

Adenine Adsorption on Gold and Graphene Surfaces

Scientists investigated how adenine, a fundamental building block of DNA, interacts with gold nanoparticles and graphene surfaces, combining computational modelling with spectroscopic techniques to understand binding and its effect on spectroscopic signatures. This work explains why certain spectroscopic signals amplify when adenine is near these nanostructures, revealing the relationship between adsorption geometry and electronic interactions. The team employed density functional theory calculations to determine preferred binding modes, calculating electronic properties and predicting vibrational spectra, accounting for the influence of the surrounding solvent for accurate modelling. By comparing calculated spectra with experimental data from surface-enhanced infrared absorption and Raman spectroscopy, researchers validated their models and gained deeper insights into the observed phenomena.

Results reveal that binding mode significantly influences spectroscopic signals, highlighting the importance of intermolecular interactions like Van der Waals forces and electronic interactions. The study also demonstrates the crucial role of the solvent in the adsorption process and spectroscopic properties, suggesting that adsorption can be influenced by external factors like applied potential. The development of an open-source code for nanoplasmonics further contributes to the field.

Multiscale Modelling of Surface Enhanced Infrared Absorption

Scientists developed a new computational framework to model surface-enhanced infrared absorption (SEIRA) spectroscopy, bridging the gap between quantum mechanical descriptions of molecules and classical models of plasmonic materials. This innovative approach accurately simulates how molecules interact with nanostructures, enabling detailed analysis of vibrational signals amplified by plasmonic effects, achieving accuracy comparable to more computationally intensive methods. The team engineered classical models, based on established principles of material science, to simulate the optical response of diverse plasmonic materials, including noble metal nanoparticles and graphene-based substrates. These models account for atomic-level details, such as edges and defects, critical for achieving strong local field enhancement, allowing for simulations of systems containing over one million atoms. Researchers applied this framework to investigate adenine adsorbed on both gold nanostructures and graphene disks, a system extensively studied experimentally and theoretically. By calculating SEIRA spectra and comparing them with experimental data and surface-enhanced Raman scattering spectra, they assessed the quality and robustness of the approach, accurately predicting vibrational responses and providing insights into signal enhancement mechanisms.

Multiscale Modelling Captures SEIRA Spectral Accuracy

Scientists have developed a new computational framework to model SEIRA spectra, achieving accuracy comparable to full quantum mechanical methods while significantly reducing computational demands. The work combines quantum mechanical descriptions of molecules with classical models of plasmonic nanostructures, enabling simulations of complex systems with over one million atoms, representing a substantial advancement in computational nanoplasmonics. The team implemented fully atomistic, frequency-dependent models to describe the plasmonic response of materials, accurately simulating the optical response of a wide range of plasmonic materials, even in the presence of structural defects or solvent effects. The researchers successfully extended this methodology to SEIRA spectroscopy, applying it to the study of adenine adsorbed on gold nanostructures and graphene disks.

Results reveal that the resulting SEIRA spectra are highly sensitive to the orientation and adsorption site of the adenine molecule, demonstrating the framework’s ability to predict subtle changes in spectral response. The computed spectra were rigorously validated against experimental data and compared with surface-enhanced Raman scattering spectra, confirming the reliability of the approach. Analysis of graphene as a SEIRA substrate showed how its structural and electronic properties modulate the molecule-graphene response in the infrared range, highlighting its potential for advanced sensing applications.

Multiscale Modelling of Surface Enhanced Infrared Absorption

This work presents a multiscale computational approach that accurately models SEIRA spectra of molecules interacting with plasmonic nanostructures. By combining quantum mechanical descriptions of molecules with classical models for the metallic or graphene-based nanostructure, the team achieved a computationally efficient method comparable in accuracy to more demanding, fully quantum calculations, accurately capturing the localized surface plasmons crucial for signal enhancement. The methodology was successfully applied to the calculation of SEIRA spectra for adenine adsorbed on both gold nanoparticles and graphene sheets. Results demonstrate the framework’s ability to predict spectral responses, influenced by factors such as molecular orientation and adsorption site, and align well with existing experimental data and surface-enhanced Raman scattering spectra.

The team also investigated graphene’s potential as a SEIRA substrate, revealing how its structural and electronic properties modulate the molecule-graphene interaction in the infrared range. The authors acknowledge that the classical treatment of the nanostructure introduces an approximation, although the chosen models demonstrate high accuracy in capturing the essential plasmonic behavior. Future research directions include extending the methodology to more complex molecular systems and exploring the influence of environmental effects on SEIRA spectra, potentially leading to improved sensitivity in molecular detection and characterization.