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An SCC-DFTB Repulsive Potential for Various ZnO Polymorphs and the ZnO-Water System
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström.
Vise andre og tillknytning
2013 (engelsk)Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, nr 33, s. 17004-17015Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

We have developed an efficient scheme for the generation of accurate repulsive potentials for self-consistent charge density-functional-based tight-binding calculations, which involves energy-volume scans of bulk polymorphs with different coordination numbers. The scheme was used to generate an optimized parameter set for various ZnO polymorphs. The new potential was subsequently tested for ZnO bulk, surface, and nanowire systems as well as for water adsorption on the low-index wurtzite (10 (1) over bar0) and (11 (2) over bar0) surfaces. By comparison to results obtained at the density functional level of theory, we show that the newly generated repulsive potential is highly transferable and capable of capturing most of the relevant chemistry of ZnO and the ZnO/water interface.

sted, utgiver, år, opplag, sider
2013. Vol. 117, nr 33, s. 17004-17015
HSV kategori
Identifikatorer
URN: urn:nbn:se:uu:diva-208368DOI: 10.1021/jp404095xISI: 000323593100028OAI: oai:DiVA.org:uu-208368DiVA, id: diva2:652346
Tilgjengelig fra: 2013-09-30 Laget: 2013-09-30 Sist oppdatert: 2019-02-19bibliografisk kontrollert
Inngår i avhandling
1. Chemistry and Physics of Cu and H2O on ZnO Surfaces: Electron Transfer, Surface Triangles, and Theory
Åpne denne publikasjonen i ny fane eller vindu >>Chemistry and Physics of Cu and H2O on ZnO Surfaces: Electron Transfer, Surface Triangles, and Theory
2015 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

This thesis discusses the chemistry and physics of Cu and H2O on ZnO surfaces, based primarily on results from quantum chemical calculations. The underlying context is heterogeneous catalysis, where Cu/ZnO-mixtures are used in the industrial synthesis of methanol and in the water gas shift reaction. Electron transfer between small Cu clusters and ZnO is central to this thesis, as are the design and use of models that can describe realistic and very large-scale ZnO surface structures while still retaining the electronic nature of the system. Method and model enhancements as well as tests and validations constitute a large part of this thesis.

The thesis demonstrates that the charges of small Cu clusters, adsorbed on the non-polar ZnO(10-10) surface, depend on whether the Cu clusters contain an even or odd number of atoms, and whether water is present (water can induce electron transfer from Cu to ZnO). On the polar Zn-terminated ZnO(0001) surface, Cu becomes negatively charged, which causes it to attract positively charged subsurface defects and to wet the ZnO(0001) surface at elevated temperatures.

When a Cu cluster on a ZnO surface becomes positively charged, this happens because it donates an electron to the ZnO conduction band. Hence, it is necessary to use a method which describes the ZnO band gap correctly, and we show that a hybrid density functional, which includes a fraction of Hartree-Fock exchange, fulfills this requirement. When the ZnO conduction band becomes populated by electrons from Cu, band-filling occurs, which affects the adsorption energy. The band-filling correction is presented as a means to extrapolate the calculated adsorption energy under periodic boundary conditions to the zero coverage (isolated adsorbate, infinite supercell) limit.

A part of this thesis concerns the parameterization of the computationally very efficient SCC-DFTB method (density functional based tight binding with self-consistent charges), in a multi-scale modeling approach. Our findings suggest that the SCC-DFTB method satisfactorily describes the interaction between ZnO surfaces and water, as well as the stabilities of different surface reconstructions (such as triangularly and hexagonally shaped pits) at the polar ZnO(0001) and ZnO(000-1) surfaces.

 

sted, utgiver, år, opplag, sider
Uppsala: Acta Universitatis Upsaliensis, 2015. s. 50
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1207
Emneord
catalysis, density functional theory, SCC-DFTB, band-filling correction
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-236302 (URN)978-91-554-9111-6 (ISBN)
Disputas
2015-01-09, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2014-12-18 Laget: 2014-11-17 Sist oppdatert: 2015-02-03

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