Density-Functional Theory, Catalysis, Ceria, Bulk Water, Gold-Oxide
We study the structure and energetics of water molecules adsorbed at ceria (111) surfaces below one monolayer coverage using density-functional theory. The results of this study provide a theoretical framework for interpreting recent experimental results on the redox properties of water at ceria (111) surfaces. In particular, we have computed the structure and energetics of various absorption geometries at stoichiometric ceria (111) surface. In contrast to experiment results, we do not find a strong coverage dependence of the adsorption energy. For the case of reduced surface, our results show that it may not be energetically favorable for water to oxidize oxygen vacancy site at the surface. Instead, oxygen vacancies tend to result in water more strongly binding to the surface. The result of this attractive water-vacancy interaction is that the apparent concentration of oxygen vacancies at the surface is enhanced in the presence of water. Finally, we discuss this problem with reference to recent experimental and theoretical studies of vacancy clustering at the (111) ceria surface. We also describe the simulation results for the structure and dynamics of liquid water using the SIESTA electronic structure approach. We find that the structure of water depends strongly on the particular basis set used. Applying a systematic approach to varying the basis set, we find that the basis set which results in good agreement with experimental binding energies for isolated water dimers also provides a reasonable description of the radial distribution functions of liquid water. We show that the structure of liquid water varies in a systematic fashion with the choice of basis set. Comparable to many other first-principle studies of liquid water using gradient-corrected density functionals, the liquid is found to be somewhat overstructured. The possibility of further improvements through a better choice of the basis set is discussed. We find that while improvements are likely to be possible, application to large-scale systems will require use of a computational algorithm whose computational cost scales linearly with system size. Finally, we study the molecular and atomic adsorption of oxygen on the gold nano-clusters. We show multiple stable and metastable structures for atomically and molecularly adsorbed oxygen to the gold cluster. We plan to predict the reaction pathway and calculate activation energy barrier for desorption of molecular oxygen from the atomically adsorbed gold cluster which is very important for any catalytic reaction occurring using gold nanoparticles.
Master of Science (M.S.)
College of Engineering and Computer Science
Mechanical, Materials and Aerospace Engineering;
Materials Science and Engineering
Length of Campus-only Access
Masters Thesis (Open Access)
Kumar, Santosh, "Density-functional Theory Applied To Problems In Catalysis And Electrochemistry" (2006). Electronic Theses and Dissertations. 918.