Investigation of the Second Harmonic Generation at the Water-Vacuum Interface by Using Multi-Scale Modeling Methods

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Surface Science

Background:

• Second harmonic generation (SHG) is a powerful nonlinear optical technique.
• Understanding interfacial properties is crucial in chemistry and materials science.
• Distinguishing interfacial signals from bulk contributions remains a challenge.

Purpose of the Study:

• To investigate the interfacial selectivity of SHG at the water-vacuum interface.
• To develop a computational model capable of separating bulk and interfacial responses.
• To accurately calculate molecular first hyperpolarizability contributions.

Main Methods:

• Combined classical molecular dynamics (MD) and quantum chemistry (QC) simulations.
• Development of a theoretical model to analyze SHG signals.
• Calculation of molecular first hyperpolarizability (β) responses.

Main Results:

• The developed model successfully distinguished between bulk and interfacial contributions to SHG.
• Demonstrated the interfacial selectivity of SHG at the water-vacuum interface.
• Provided accurate calculations of molecular hyperpolarizability at the interface.

Conclusions:

• The computational approach provides a reliable method for studying interfacial nonlinear optics.
• This work advances the understanding of molecular responses at interfaces.
• The findings have implications for surface characterization and molecular design.