Surface energy and excess charge in (1×2)-reconstructed rutile TiO2(110) from DFT+U

Abstract

Physically reasonable electronic structures of reconstructed rutile TiO2(110)-(1×2) surfaces were studied using density functional theory (DFT) supplemented with Hubbard U on-site Coulomb repulsion acting on the d electrons, so called as the DFT+U approach. Two leading reconstruction models proposed by Onishi-Iwasawa and Park et al. were compared in terms of their thermodynamic stabilities.PACS numbers: 71.15. Mb, 68.47.Gh Rutile TiO 2 and its surfaces represent model systems to explore the properties of transition metal oxides that are important in technological applications such as catalysis, photovoltaics, and gas sensing [1], to name a few. Truncated or stoichiometric (110) surface of rutile is the most stable one among all surfaces of titania [2]. Upon thermal annealing or ion bombardment TiO 2 (110)-(1×1) surface is reduced by loosing the bridging oxygens, and is often undergo a (1×2) reconstruction with row formations [3][4][5][6][7][8][9][10][11][12][13]. The identification of these rows on reconstructed surfaces, in three dimensions, is difficult by experimental methods [13]. The best candidate for modeling this reconstruction involves the addition of "Ti 2 O 3 " molecule on the surface unit cell (added-row model) proposed by Onishi and Iwasawa [3]. In addition to theoretical studies it was supported by electron stimulated desorption of ion angular distribution (ESDIAD), scanning tunnelling microscopy (STM), and low-energy electron diffraction (LEED) experiments [5][6][7][8][9][10][11]. On the other hand, Shibata et al. Now there is a debate about which formation gives rise to the (1×2) long range order, the last proposed one or the best previous candidate? In this context we study the electronic properties of these two models using Hubbard U corrected total energy density functional theory (DFT+U ) calculations to get physically reasonable results comparable to existing experimental data. We discuss which of these leading models can be assigned to describe the (1×2) reconstructed surface by comparing them according to their thermodynamic stabilities.Band structures of reduced and reconstructed TiO 2 (110) surfaces determined by pure DFT calculations does not agree with experiments [10,14,15]. Failure of the standart DFT is not limited to band-gap underestimation stemming from the many-electron self-interaction error (SIE). More importantly, it does not predict experimentally observed gap states [16,17] that are associated with the excess electrons due to the formation of surface oxygen vacancies. In DFT calculations, these Ti 3d electrons occupy the bottom of the conduction band (CB) giving metallic character. Hence, hybrid DFT methods need to be used. For instance, SIE can be partly corrected by partially mixing nonlocal Fock exchange term with DFT exchange term [18,19] or DFT+U approach [20] can make up for the lack of strong correlation between the 3d electrons, a shortcoming of common exchange-correlation functionals. Empirical Hubbard U term accounts for the on-site Coulomb repulsion between th...

Electronic structures of bare and terephthalic acid adsorbed TiO2(110)-(1 × 2) reconstructed surfaces: origin and reactivity of the band gap states

“…Very recently, López et al 19 paid particular attention to the study of the electronic structures of the TiO 2 (110)-(1 Â 2) surface and identified for the first time an asymmetric feature of the band gap states (BGSs) due to the mixed contributions among bulk defects and surface Ti 2 O 3 -terminations. 20,21 These calculation results are not in agreement with the reduced dispersion experimentally observed by angle resolved photoelectron spectroscopy experiments for the gap states of the (1 Â 2) surface. 20,21 These calculation results are not in agreement with the reduced dispersion experimentally observed by angle resolved photoelectron spectroscopy experiments for the gap states of the (1 Â 2) surface.…”

“…It has been reported that TPA molecules in a bulk phase start to sublimate at B380 K, 49 while benzoate species chemically adsorbed on TiO 2 decompose above 650 K. 50 In addition, the two neighboring surface hydroxyl groups on the TiO 2 recombine to produce water at B490 K with simultaneous regeneration of an oxygen vacancy. Unal et al 21 calculated the surface energy and the excess charge of the (1 Â 2)-reconstructed TiO 2 (110) surface using the (DFT+U) approach. The curve (i) in Fig.…”

“…The geometry of the bare TiO 2 (110)-(1 Â 2) surface was optimized neglecting bulk defects. 20,21 Looking at the calculations, the presence of a split BGS at a binding energy of 0.5 eV is also interesting. Fig.…”

Valence band electronic structure characterization of the rutile TiO2 (110)-(1×2) reconstructed surface

“…This discrepancy has been associated to the tendency of the GGA functional [30] to overestimate the delocalization of states that may be otherwise localized by different factors, like correlation effects and the quasi-1D character of states running along the reconstruction chains. Indeed, the use of GGA+U as an alternative exchange and correlation functional favors the opening of a gap along the [001] direction and results in a dispersive state in the band gap, localized at the subsurface Ti atoms in the trenches between the Ti 2 O 3chains[31,32].Figure 3shows the computed valence band electronic structure for a slab (left) and the corresponding projection of bulk states along the GΓ-Z direction (right). Blue dots label states with more than an 80% contribution from atoms of the Ti 2 O 3 chains, while green dots represent the same for atoms located on the TiO 2 tri-layer closest to the surface.…”

Metalation of tetraphenylporphyrin with nickel on a TiO2(110)-1 × 2 surface

“…55 Ünal et al proposed that the Ti 2 O 3 structure is more stable than the Ti 2 O structure on the basis of DFT+U calculations. 56 The Ti 2 O 3 added row appears as bright stripes along the [001] direction, as shown in Fig. 1b.…”