Synthesis of {111}-Faceted Au Nanocrystals Mediated by Polyvinylpyrrolidone: Insights from Density-Functional Theory and Molecular Dynamics

We use density-functional theory (DFT) and molecular dynamics (MD) to resolve the role of polyvinylpyrrolidone (PVP) in the shape-selective synthesis of Au nanostructures. Using DFT, we probe the adsorption-induced surface energies and spatially resolved binding of PVP monomer analogs on Au(111), Au(100), and (5 x 1) Au(100)-hex. These calculations suggest that {111} facets should be prevalent in Au nanostructures grown with the help of PVP. We explore the role of solvent and find that, while solvent weakens binding, it does not change the trends we observe in vacuum. We fit an ad hoc interatomic potential to the DFT results so we can describe the binding of PVP to the Au surfaces. Using MD simulations based on this potential, we investigate the PVP-induced surface energies, PVP binding affinities, and oxygen density profile of atactic PVP icosamers on Au(111) and (5 x 1) Au(100)-hex. We conclude that {111}-faceted Au nanocrystals are preferred in PVP-mediated synthesis of Au nanostructures. The reconstruction of Au(100) is important in achieving {111}-facet selectivity.