Tag Archives: Thomas Frauenheim

Self-Consistent-Charge Density-Functional Tight-Binding (SCC-DFTB) Parameters for Ceria in 0D to 3D

Authors: Jolla Per Kullgren, Matthew Jason Wolf, Kersti Hermansson, Christof Köhler, Bálint Aradi, Thomas Frauenheim, and Peter Broqvist

Reducible oxides such as CeO2 are challanging to describe
with standard density functional theory (DFT) due to the mixed valence states of the cations, and often require the use of additional correction schemes, an
d/or more computationally expen- sive methods. This adds a new layer of complexity when it comes to the generation of Slater-Koster tables and the corresponding repulsive potentials for self-consistent density functional based tight binding (SCC-DFTB) calculations of such materials. In this work, we provide guidelines for how to set up a parameterisation scheme for mixed valence oxides within the SCC-DFTB framework, with a focus on reproducing structural and electronic properties as well as redox reaction energies calculated using a reference DFT method. This parameterisation procedure has been used to generate parameters for Ce–O interactions, with Ce in its +III or +IV formal oxidation states. The generated parameter set is validated through comparison to DFT calculations for various ceria (CeO2) and reduced ceria (CeO2−x ) systems of different dimensionalities ranging from 0D (nano-particles) to 3D (bulk). As oxygen vacancy defects in ceria are of crucial importance to many technological applications, special focus is directed towards the capability of describing such defects accurately.

J. Phys. Chem. C2017, 121 (8), pp 4593–4607
DOI: 10.1021/acs.jpcc.6b10557

An SCC-DFTB Repulsive Potential for Various ZnO Polymorphs and the ZnO-Water System

Authors: Matti Hellström, Kjell Jorner, Maria Bryngelsson, Stefan Ernest Huber, Jolla Per Kullgren, Thomas Frauenheim, and Peter Broqvist

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 nano-wire systems as well as for water adsorption on the low-index wurtzite (10-10) and (11-20) 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.

J. Phys. Chem. C, 117, 17004 (2013).
DOI: 10.1021/jp404095x