Comparison of density functional theory methods as applied to compound semiconductor-oxide interfaces: Slab versus cluster models

Abstract

The comparison of density functional theory cluster and slab approaches is presented for modeling the formation of electrically pinned and unpinned metal oxide-III/V semiconductor interfaces. Thermodynamic stability, interfacial electrical properties, interfacial charge trap formation and bonding structures are examined critically in the case of gallium oxide formation on the GaAs(001)-β2(2×4) surface via direct oxidation of the surface with thermal O2(g) and by vapor deposition of Ga2O(g). It is seen in both cluster and slab models that the direct oxidation with thermal O2 will lead to an electrically pinned surface, while vapor deposition of Ga2O will electrically passivate the surface, effectively unpinning the interface. Fermi-level pinning and unpinning is observed in the local density of states (DOS) in the band-gap region, in the charge distribution per surface atom, and in the geometric structures. It is seen that the DOS can be accurately predicted using either cluster or slab DOS. When cluster DOS is calculated, band-gap states appear delocalized due to poor global convergence caused by the finite cluster size effect. The thermal smearing factor for the density of states needs to be decreased from the typical value of 0.2–0.1 eV to compensate for poor convergence to reproduce accurate DOS. While cluster and plane-wave slab models predict the experimentally observed phenomenon, the slab models more accurately predict the reaction thermodynamics. We have compared both linear combination of atomic orbital (LCAO) clusters to plane-wave slab models and plane-wave clusters to plane-wave slab models to investigate the most critical parameters in attaining accurate results. It is seen that both the LCAO and plane-wave cluster models are poorly converged with respect to total energy due to the finite cluster size effect, causing over 1 eV error in the total energy.

Ab Initio Theoretical Study of Substituted Dicarboxylic Acids Adsorbed on GaAs Surfaces: Correlation between Microscopic Properties and Observed Electrical Behavior

“…The positions of all the heavy atoms in the first five layers (counting from bottom) were frozen in their bulk values, so that only the geometry of the two top As and Ga layers and of O and H atoms was allowed to relax. Recently, a similar approach (DFT calculations on the same cluster) was used to study the electronic properties of the GaAs oxidized surface, finding a good agreement with the results obtained with plane waves on periodic slabs …”

“…Recently, a similar approach (DFT calculations on the same cluster) was used to study the electronic properties of the GaAs oxidized surface, finding a good agreement with the results obtained with plane waves on periodic slabs. 50 Localized charges in the molecule-on-cluster systems were computed according to the Hirshfeld procedure. 51…”

C–H activation and metalation at electrode surfaces: 2,3-dimethyl-1,4-dihydroxybenzene on Pd(pc) and Pd(111) studied by TLE, HREELS and DFT

“…A slab model was used since it overcomes many of the difficulties faced in cluster models. 29,30 The adsorption energy (E ads ) determines the relative stabilities of the adsorption structures and is defined as:…”

Exploiting the locality of periodic subsystem density-functional theory: efficient sampling of the Brillouin zone

“…When applying periodic boundary conditions, a perfectly crystalline surface is obtained. Even though slab models are preferred to cluster models [23][24][25][26], they are not free of pitfalls. For DFT calculations to be time effective, a cell can only contain a small number of independent atoms [27][28][29], and slabs will have limited thickness (usually four or five atomic layers) with a surface featuring only a handful of independent atoms.…”