(66g) Understanding Molecular Interactions and Interfaces with Computational Spectroscopy

Many technologies depend on the interfaces between two materials. Examples include the colloidal interface, which can be engineered for specific self-assembly behaviors, and water-hydrophobic interfaces, which can be used to catalyze reactions in confined water droplets. However, interfacial length scales pose challenges for understanding interfaces in both experiment and simulation, hindering our ability to design more effective ones. Here, we used first-principles electronic structure calculations to design a spectroscopic model (the "monomer-field model") for use in combination with molecular simulation. Our model uses the intermolecular electric fields measured to predict Raman spectra, which we demonstrate for liquid water. The physics-based nature of our model enables us to attribute spectral behavior to specific physical phenomena, like strengthened or weakened hydrogen-bonding, and makes it extensible to different environments, like interfaces. We use our model to probe the behavior of liquid water, finding that the structural order in the liquid combines with Fermi resonance to yield complex features in the spectra. We then apply our model to the interface of an oil-in-water emulsion, finding the presence of a strong electric field, which has large implications for reactivity at such interfaces.