Clusters and Surfaces in Reactive Atmospheres at Realistic Conditions: Beyond the Static, Monostructure Description*

The processes occurring at surfaces play a critical role in the manufacture and performance of advanced materials, e.g., electronic, magnetic, and optical devices, sensors, and catalysts. A prerequisite for analyzing and understanding the electronic properties and the function of surfaces is detailed knowledge of the atomic structure, i.e., the surface composition and geometry under realistic gas-phase conditions. The key quantity for studying the structure and function of surfaces/clusters in reactive atmospheres is the Gibbs free energy, as function of number of particles, pressure, and temperature. Here, I present a set of methods for the sampling of the configurational space of (nano)clusters and surfaces in reactive (e.g., O2, H2) atmosphere, in the canonical and grand-canonical ensembles, aiming at the unbiased determination of the phase diagrams as function of temperature and partial pressure of the reactive gas. A common trait of the analysis of the dfferent systems is the description of ensembles of structures as function of envornmental variables, i.e., the identification of the invariant, permanent features, within the "noise" of continiously transforming ones.
Applications to gold and metal-oxide nanoclusters, and silicon surfaces, described with first-principles potential-energy surfaces, will demonstrate the insight gained by the direct access to observables at finite temperature and pressure.