Title:	Water interactions on the Cuprite surface
DNr:	SNIC 2015/1-116
Project Type:	SNIC Medium Compute
Principal Investigator:	Tore Brinck <tore@kth.se>
Affiliation:	Kungliga Tekniska högskolan
Duration:	2015-03-31 – 2016-04-01
Classification:	10407 10403 10402
Keywords:

Abstract

We apply for computational resources as a part of a project of studying the interface of cuprous oxide (Cu2O) and water. Using electronic structure programs and density functional theory (DFT), we have identified a number of important states for the redox processes on the Cu2O(100) surface. The aim of the current application is to extend the project. Firstly, we intend to study the redox processes at larger water coverage, up to a full monolayer and possible beyond, in order to better represent conditions in real applications. Secondly, we would like to consider a larger surface model to be able to reflect experimentally observed symmetry patterns as well as to avoid spurious computational effects due a too small model size. Finally, we plan an evaluation on the choice of computational method. More specifically, we intend to test the performance of different exchange-correlation functionals. This will be performed as a benchmark against experimental data for future reference. Studying copper oxides in an aqueous ambient is of interest for a number of reasons. Cuprous oxide (Cu2O) is, for instance, a common catalytic material. Additionally, in most real applications, metallic copper will be covered by an oxide film and exposed to humid air. Hence understanding of the water¬-oxide interface is essential for copper applications in various fields, including, for instance, microelectronics, energy transmission and construction engineering. A specific motivation for the current study is, moreover, to shed light on recent and unexplained observations of hydrogen gas evolution from copper samples immersed in oxygen free water. The latter is a question of profound importance in the debate on the long-¬term storage of spent nuclear fuel. At this stage of the project, focus is directed at evaluating the thermodynamic relation between different states of surface wetting, hydroxylation and oxidation. In order to do this with confidence, the computational method of choice must be carefully chosen by calibration against experimental data. We plan to evaluate the performance of a number of different DFT-¬functionals including GGA (PBE), hybrid (HSE06), and van der Waals corrected functionals (PBE-D3 and optB88-vdW). In addition, we will consider DFT+U functionals. The use of hybrid functionals has proven to be a great improvement for the description of chemical reactions, but is not commonly applied in studies of materials and surfaces. Moreover, DFT does in general have difficulties in describing dispersion interactions. Some relatively recent van der Walls functionals include corrections to overcome this general problem. The use of hybrid and van der Waals corrected functionals in this project is anticipated to improve the validity of our computations and aid in the understanding of the important interplay between water and oxide surfaces. We apply for a medium size project since we believe that the scope of our project motivates such an allocation. Moreover, if an appropriately sized model is to be studied, the use of hybrid functionals will demand allocations larger than those provided for the small projects.