Surface properties of clean and Au or Pd covered hematite (α-Fe₂O₃) (0001)

Abstract

The structure and electronic properties of different terminations of the α-Fe(2)O(3)(0001) surface were studied with spin-polarized density functional theory (DFT) and the DFT + U method accounting for the effect of strong on-site Coulomb correlations. The results for lattice relaxation, electronic and magnetic properties are presented and discussed. Though the DFT and DFT + U methods provide qualitatively very similar surface geometries they differ very much in the prediction of the electronic and magnetic properties, and the surface energetics of the clean α-Fe(2)O(3)(0001). The most stable single iron terminated (0001) surface and the oxygen-rich termination were chosen to study Au and Pd atom adsorption. The results show that both Au and Pd bind strongly to hematite surfaces and induce large changes in their geometry. The DFT + U bonding is weaker by 0.3-0.6 eV than DFT on the iron terminated surface and about 2 eV stronger on the oxygen terminated one. The binding is stronger for Pd than Au and for both adsorbates is distinctly stronger at the oxygen than at the iron terminated surface. On the iron terminated surface the adsorption binding energy per adatom increases both with Au and Pd coverage, whereas for the oxygen terminated one the opposite trend is observed.

A Density Functional Theory Study of the Adsorption of Benzene on Hematite (α-Fe2O3) Surfaces

“…The calculated lattice parameters a = b = 5.024 Å and c = 13.658 Å are also in good agreement with experiment [1]. Rohrbach et al [54] and Bandyopadhyay et al [56] have also shown that the DFT+U method (U-value = 5 eV) provides a good description of the band-gap and magnetic moment of Fe in hematite and chromia (Cr 2 O 3 ) and our calculated gap width and Fe magnetic moments compares very well with the results of other recent theoretical calculations [137,138]. In Figure 4, we show how the electronic band-gap increases with increasing strength of the on-site Coulomb repulsion, where U = 5 eV predicts the gap width (2.1 eV), which falls within the experimental range (shaded area).…”

DFT+U investigation of the catalytic properties of ferruginous clay

“…In each of these cases, apart from in the examination of the bulk and surface structures and properties of mackinawite, it was found that the addition of a Hubbard parameter produced more physically realistic results compared to the computations without this parameter. Although there are many examples of the application of DFT+U for iron-bearing minerals demonstrating the necessity of 5 the inclusion of the Hubbard parameter, (Devey et al 2009;Hsu et al 2010;Kiejna and Pabisiak 2012;Stashans et al 2012) and its importance in the investigation of transition metal oxide surface/interface interactions is well-established, (Nolan et al 2006(Nolan et al , 2008(Nolan et al , 2012Branda et al 2010;Szabová et al 2010) the application to date, of the Hubbard parameter to clay minerals appears to be in its infancy, with our study apparently among the first in this particular field.…”

Structure–Activity Relationship of Iron Oxides for NO Reduction in the Presence of C3H6, CO, and O2

“…On‐site Coulombic repulsion on localized 3 d electrons was considered by the GGA+ U approach, with U eff =4.0 for Fe . Slab models of α ‐Fe 2 O 3 (0001) and Fe 3 O 4 (111) were created by cutting their optimized bulk models. The initial spin arrangements in α ‐Fe 2 O 3 and Fe 3 O 4 were set to be antiferromagnetic and ferrimagnetic, respectively.…”