Atomistic insights into surface reactivity via density functional theory

Download
2018
Demirtaş, Merve
In this thesis, three different topics are investigated by using Density Functional Theory. First, an extensive study of the water gas shift reaction on Mo2C surface is carried out. CO is chosen as a probe molecule in order to understand the structural and electronic effects of the metal additives on the surface. We show that preadsorbed K atom enhences the activation and adsorption of CO molecule on the surface when compared to precious metal additives we consider, which are Pt and Au. Additionally, the presence of Pt and K stabilizes the transition state of the C-O bond scission, lowers the activation energy of this reaction. In the fourth part, the oxidation of CH3OH molecule is examined on bare and Ptdoped Au(111) surfaces. With this aim, the adsorption energies of molecules and atoms involved in the reaction of CH3OH dissociation to CH3O and H in order to obtain their stable sites. Having defined them, the activation barrier calculations are carried out on the bare Au(111) surface. Additionally, the same calculations are performed on the Pt-doped Au(111) surface in different concentrations in order to see the effect of them on the activation barrier. We show that the activation barriers are notably decreased when the number of Pt dopant atoms on the surfaces increases. In the fifth part, the interaction between the amorphous SiO2, crystal Si, oxidized crystal Si surfaces and ions of different types of etchants, which are H,F and Cu, is examined. The interaction between ions and amorphous surface is shown to be weaker than the reconstructed bare and oxydized Si surfaces. The adsorption energies are quite high for H and F ions on the reconstructed Si(001) surface. For Cu ions, the adsorption energy is improved with precovered O atom on the Si surface.

Suggestions

Modeling and Predicting Surface Roughness via Transformation Optics
Ozgun, O.; Kuzuoğlu, Mustafa (2014-08-28)
Monte Carlo analysis of surface roughness in electromagnetic scattering problems is presented by using the principles of transformation electromagnetics/optics in finite methods. The main motivation in the proposed approach is to eliminate the need of mesh generation for each surface in repeated Monte Carlo realizations, and hence, to devise a faster model in predicting surface roughness. A single, simple and uniform mesh is employed assuming a smooth surface and ignoring the actual surface, and thereafter,...
Density functional theory calculations of small ZnmSn clusters
Katırcıoğlu, Şenay (2001-07-16)
We have investigated the structural and electronic properties of isolated neutral ZnmSn clusters for m + n less than or equal to 4 by performing density functional theory calculations at B3LYP level. We have obtained the optimum geometries, the electronic structures, and the possible dissociation channels of the clusters considered.
Density functional theory investigation of TiO2 anatase nanosheets
Sayın, Ceren Sibel; Toffoli, Hande; Department of Physics (2009)
In this thesis, the electronic properties of nanosheets derived from TiO2 anatase structure which acts as a photocatalyst, are investigated using the density functional theory. We examine bulk constrained properties of the nanosheets derived from the (001) surface and obtain their optimized geometries. We investigate properties of lepidocrocite-type TiO2 nanosheets and nanotubes of different sizes formed by rolling the lepidocrocite nanosheets. We show that the stability and the band gaps of the considered ...
Molecular orbital treatment of some endohedrally doped C-60 systems
Türker, Burhan Lemi; Gumus, S (Informa UK Limited, 2006-03-01)
The present review article is a collection of the theoretical studies about some endohedrally doped C-60 systems, based on density functional theory and ab initio calculations. The energies of the composite system, as well as molecular orbital energies depend on the type of dopant, symmetry of the system and the spin state. In the case of C@ C-60, the dopant interacts with the cage depending on the symmetry and spin state, whereas in Be@ C-60, Be is found to be unbound. In certain cases ( as Ca, Sc and Y) t...
Oscillation of integro-dynamic equations on time scales
Grace, Said R.; Graef, John R.; Zafer, Ağacık (2013-04-01)
In this paper, the authors initiate the study of oscillation theory for integro-dynamic equations on time-scales. They present some new sufficient conditions guaranteeing that the oscillatory character of the forcing term is inherited by the solutions.
Citation Formats
M. Demirtaş, “Atomistic insights into surface reactivity via density functional theory,” Ph.D. - Doctoral Program, Middle East Technical University, 2018.