Density Functional Theory Investigations of Surface Structure and Reactivity
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- Institutt for fysikk 
The Cr2O3(0001) surface is assumed to terminate by chromium atoms, chromyl groups, and oxygen atoms. This essentially models the industrial surface when subjected to different oxygen chemical potentials. The issue of high temperature surface states is also of particular importance concerning various effects such as corrosion. The investigation of the interaction of selected atomic adsorbates, paper I, has not only been important from a fundamental physics point of view, but also offered useful insight on applied subjects such as corrosion. Various diatomic molecules, paper II, are found to show different reactivities to the Cr2O3(0001) surface. The different terminations provide insight on the reactivity of the surface to the molecules under varying oxygen chemical potential as background environment. Various chemical complexes have been investigated, each having applications in chemical catalysis, including the growth of an H2O layer in a hexagonal 2D lattice and an array of Cl atoms in a honeycomb lattice. Poisoning of materials by sulfuric acid is among the daily problems worldwide, with significant loss of resources. A mechanistic design on how to avert the problem is at the heart of scientific activities. This study, paper III, investigates the interaction of molecular, intermediately decomposed, and fully decomposed states of H2S with the Cr2O3(0001) surface, allowing for the possibility of a varying oxygen chemical potential as background environment. Based on the difference in reactivity of the adsorbate species with the differently terminated surfaces, we have suggested that a higher oxygen chemical potential as background environment has a potential to be unreactive to the adsorbate species or at least minimize the surface poisoning. Titanium-nickelide is an important biomaterial with various applications in medical technology. However, it is still a matter of a continued research effort on how to establish the best biocompatible version of the material. Existence of nickel atoms at contact points of the biomaterial has been reported to hamper the quality of the biomaterial. As a consequence, several experimental activities have been carried out to remedy a surface treatment of the material, mostly by oxidation. This study, paper IV, characterizes the oxidation of various low indexes of the biomaterial surface. Based on this characterization, a conclusion is reached that doping the material with potassium atoms improves the performance quality of the biomaterial and a method of achieving the doping is suggested. The use of two or more DFT packages, with different basis sets, may be motivated for consistency verification of results obtained so as to make quality conclusions, or to take advantage of a reduced computational time. In this report, paper V, we have shown that the Dacapo DFT package and the BAND DFT package with very different basis sets, i.e., plane waves and atomic orbitals, respectively, can be used together in a single study by satisfying the above motivation points. We have reported that the pseudopotentials (frozen cores) used in the calculations play a crucial role for the outcome of calculations and computation time demand, and suggested a possible discrepancy in the magnitudes of energy differences. The alloy between rare earths and novel transition metals Pt and Pd is of renewed research interest. This is in part motivated by the desire to tailor some of the properties of these widely applied transition metals or the rare earths. To be able to have control over the quantitative changes in the properties, a clear establishment of the alloy structures is crucial. There have been considerable experimental research efforts carried out reporting the investigated alloy structures. However, a consistent conclusion has not been obtained. This study, paper VI, is based on the various experimentally predicted structures and systematically suggests the most stable structure.
Has partsNigussa, K.N.; Nielsen, K.L; Borck, Ø.; Støvneng, J.A.. Adsorption of hydrogen, chlorine, and sulfur atoms on α-Cr2O3(0001) surfaces: A density functional theory investigation. . 53(11): 3612-3622, 2011. 10.1016/j.corsci.2011.07.005.
Nigussa, K.N.; Borck, Ø.; Støvneng, J.A; Nielsen., K.L.. Adsorption of H2, Cl2, and HCl molecules on α-Cr2O3 (0001) surfaces: A Density Functional Theory investigation.. .
Nigussa, K.N.; Borck, Ø.; Støvneng., J.A.. Adsorption of H2S on α-Cr2O3(0001) surfaces: A Density Functional Theory investigation. .
Nigussa, K. N.; Stovneng, J. A.. Oxidation of pure and potassium-doped NiTi shape memory surface. Physical Review B. Condensed Matter and Materials Physics. (ISSN 1098-0121). 82(24): 245401, 2010. 10.1103/PhysRevB.82.245401.
Nigussa, K. N.; Stovneng, J. A.. Theoretical investigation of the interaction of oxygen with pure and K-doped NiTi shape memory surface alloys. Computer Physics Communications. (ISSN 0010-4655). 182(9): 1979-1983, 2011. 10.1016/j.cpc.2010.12.027.
Nigussa, K.N.; Støvneng., J.A.. Alloy structure of rare earth Ce with Pt base metal, and the adsorption of CO.. .