Embedded-Cluster Calculations in a Numeric Atomic Orbital Density-Functional Theory Framework

Daniel Berger
Technical University Munich (TUM)

Nanostructured oxide surfaces promise a wide range of applications in surface chemistry and catalysis. Exploring the zoo of combinatorial compound material for the ultimate candidate for a certain application may best be tackled by computational studies. When addressing those functionalities through quantitative first-principles calculations, applying periodic boundary conditions (PBC) becomes numerically inefficient or even unfeasible at a certain system size, especially when going beyond the semi-local DFT level of theory. Exploiting the localized character of those systems we develop a highly efficient embedding setup to overcome limitations through system size. In this setup the nanostructure and immediate oxide surrounding is described quantum mechanically, while the long-range electrostatic interactions with the support are accounted for through a monopole field. A transition shell between both regions is introduced to prevent electron leakage into the Coulomb singularities and wrong chemical behavior through the creation of dangling bonds at the boundary of the quantum mechanical (QM) zone. In this transition shell oxide particles are represented through norm-conserving pseudopotentials [1] in the fully separable Kleinman-Bylander form [2]. We report details of the implementation of this scheme into the FHI-aims package. Not being restricted to PBC calculations, the developed set-up is ultimately also capable to efficiently deal with charged states, which will be a fundamental asset for the description of charge transfer processes e.g. in photoinduced catalysis. We illustrate the performance of various levels of theories using the water-splitting reaction at ideal and defected TiO2 (110) surfaces as showcase.
[1] M. Fuchs and M. Scheffer, Comput. Phys. Commun. 119, 67-98, (1999).
[2] L. Kleinman and D. M. Bylander, Phys. Rev. Lett. 48, 1425-1428, (1982).

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