Using Computational Techniques and Simulations to Analyze M+(H2O)n Clusters, Structures and Interactions Using the i-TTM Model and Many-Body Molecular Dynamics

Undergraduate #35
Discipline: Chemistry and Chemical Sciences
Subcategory: Chemistry (not Biochemistry)

Achombom (Jude) Tunyi - University of Washington
Co-Author(s): Pushp Bajaj and Francesco Paesani, University of California, San Diego, La Jolla, CA

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Aerosols, tiny particles including alkali metal ions that get suspended in the atmosphere, can be detrimental to the climate, sunlight absorbance and even add to the pollution of Earth. Aerosols can be a result of volcanic eruptions, seawater being released to the atmosphere or they can be man-made. It is crucial to understand how these metallic ions hydrate with the water vapor particles present in the atmosphere on a molecular level. This will allow us to better predict the result of aerosol activity such as decreased sunlight or increased groundwater pollution. After extensive literature review, I believe that on a molecular level metallic ion aerosols will have stronger interactions with increasing size as well a vibrational spectroscopy corresponding with experimental M+ (H2O)n studies. Structures for the alkali metal ions and water clusters are made using the ion-Thole-type model (i-TTM) and many-body molecular dynamics, which performs more accurate quantum mechanical calculations by taking into account dispersion, repulsion, and electrostatic interactions. After the structures of the different isomers of the M+(H2O)n clusters were isolated, harmonic and anharmonic vibrational frequencies were calculated. These structures and frequencies were then compared to experimental results as a way of either validating or refining the model. If the molecular simulations and experimental analysis are in agreement, then potential energy surfaces can be created from the data. The findings suggest that the iTTM model is a good tool for predicting the interactions of the M+(H2O)n clusters and there are strong interactions between the alkali ions and the water clusters.

Funder Acknowledgement(s): CAICE (Center for Aerosol Impacts on Climate and the Environment) Program, NSF Center for Chemical Innovation

Faculty Advisor: Francesco Paesani, fpaesani@ucsd.edu

Role: I worked on the entire project from start to its current place from getting the simulated cluster structures to getting the frequency calculations. However, the codes and the model that allowed me to do this work was already in place when I began on the project.