Multi-scale theory and simulation of shape-selective nanocrystal growth

Capping agents, or structure-directing agents (SDAs), play a central role in the shape-selective, solution-phase synthesis of metal nanocrystals-although their exact role in many syntheses remains elusive. In this Highlight, we discuss, using the example of PVP-mediated synthesis of Ag nanocrystals in the polyol process, how multi-scale theory and simulation can lead to an understanding of how SDAs actuate nanocrystal growth. First-principles DFT calculations provide insight into the adsorption energetics of SDA molecules on metal surfaces and a comparison of DFT to experiment confirms the adage that SDA molecules promote nanocrystals with facets to which they bind the most strongly. To study aspects of solution-phase syntheses under experimental conditions, we introduced the metal-organic many body (MOMB) force field, which has high fidelity to DFT results. Using molecular dynamics simulations based on the MOMB force field, we showed how stronger PVP binding to Ag(100) leads to a lower Ag flux to this surface relative to Ag(111) and how this promotes {100}-facetted kinetic Wulff shapes, consistent with experiment.