Adsorbate Induced Reconstructions of Metal Surfaces

<p>In this dissertation I present work on the modeling of adsorbate-metal interactions with a specific focus on carbon monoxide (CO) induced restructuring of platinum stepped surfaces. Additionally, I will present work on the development of a multiple-minima fluctuating charge (mm-FlucQ) potential which has been used to simulate charge responsive platinum surfaces.</p><p>New Pt-CO and Au-CO forcefields were developed to study coverage-dependent restructuring of high-index platinum & gold (557) surfaces. It was observed that the weak Au-CO binding led to minimal disruption of the surface, whereas the strong Pt-CO interactions resulted in significant disruption of the step-edges which led to increased step-wandering. Specifically, the strong CO-CO quadrupolar repulsion caused an increase in adatom mobility. This increased mobility eventually led to large-scale surface reconstructions including the formation of a metastable double layer.</p><p>A platinum/palladium (Pt/Pd) (557) surface was simulated to explore CO-induced reconstructions on a more complicated bimetallic surface. The Pt-CO forcefield was retuned while a new Pd-CO forcefield was developed. The difference in binding strengths was found to play an important role in the disruption of the Pt/Pd surface while the preferred binding sites on each system (Pt: atop, Pd: bridge/hollow) led to significantly different behaviors with regards to surface diffusion and mobility.</p><p>The importance of step-edge energetics for the formation of adatoms encouraged us to directly examine straight edged (557) & (112) and kinked edged (765) & (321) platinum surfaces. As expected, the systems with rougher edges experienced a greater amount of surface diffusion and a concomitantly increased amount of step-wandering. The length of the (111) plateaus between step edges also played an important role with regard to the extent of surface reconstruction observed.</p><p>Accurate treatment of the electrostatic interactions between adsorbates and surfaces is often neglected in molecular dynamics simulations because of the increased computational cost and difficulty of implementation. Our new mm-FlucQ potential allows us to more properly describe a metal surface’s response to impinging charged species in a dynamic fashion by allowing the charges on each atomic site to fluctuate in response to the local electronic environment. </p>