J. Z. Zhao

Comment on "Interplay between Water and TiO2 Anatase (101) Surface with Subsurface Oxygen Vacancy".

In a recent Letter, Li and Gao [1] suggested that H2O adsorption on an anatase TiO2 (101) surface will reverse the relative stability of surface and subsurface oxygen vacancies (VOs). This reversal will cause subsurface VOs to diffuse towards the surface with a near zero potential barrier and the so-formed surface VOs will dissociate water molecules adsorbed on the surface through a barrierless pathway. In the calculations of Ref. [1], they have used a slab comprised of three composite (O-Ti-O) layers. While atomic positions within the top two composite layers are allowed to relax, atoms in the bottom composite layer are held fixed to mimic the bulk structure. In this Comment, we wish to point out that the reversal in relative stability reported in Ref. [1] is an artifact caused by an insufficient number of layers included in the slab model. The three layer model with a bottom layer fixed [1] gives a wrong description of the relative stability. Results with sufficient layers show that the reported reversal does not occur. Furthermore, claims made in Ref. [1] of novel direct and indirect interplay between subsurface VOs and adsorbed water molecules are not observed in recent experiments [2]. Such discrepancies disappear when converged numbers of layers are used [3]. We have performed calculations using Perdew-BurkeErnzerhof (PBE) functional [4] implemented in the VASP [5,6]. A plane-wave cutoff energy of 500 eV and 3 × 3 × 1 k mesh are used. We have used the optimized bulk lattice parameters of a 1⁄4 3.78 and c 1⁄4 9.58 Å to build slab models with various thicknesses: (a) a three layer slab with the bottom layer fixed, i.e., the slab used in Ref. [1]; (b) a six layer slab with the bottom four layers fixed; (c) a six layer slab with the bottom layer fixed; (d) six layers without a fixed layer; (e) a nine layer slab with the bottom layer fixed; and (f) a nine layer slab without a fixed layer. In addition, to confirm the PBE results, much more accurate HSE06 calculations [7] have been performed, as shown in Table I. From Table I, we see that both the HSE06 and PBE calculations give the same conclusion. The results show that if only the two top layers are allowed to relax in slab (a) and that of Ref. [1], the system with subsurface VOs is indeed less stable than that with surface VOs, and the reported reversal does exist. Our calculated energy difference is 0.19 eV compared to 0.18 eV reported in Ref. [1], indicating that the two calculations obtain similar results if the same slab model is used. Increasing the layer number to six but still only allowing the top two layers to relax, i.e., slab (b), the reversal still exists and the energy difference is 0.23 eV (see Table I). However, the reversal disappears if more layers are allowed to relax, e.g., in slab (c) where the top five layers are allowed to relax. The energy difference becomes −0.12 eV, indicating that the system with subsurface VOs now is more stable. Increasing the slab thickness to nine layers with (e) and without (f) a fixed bottom layer shows little further change in the energy difference. Thus, the result of slab (c) has converged. The slab model used in Ref. [1] also leads to gross underestimates of energy barriers involved in water dissociation pathways. Based on the erroneous barriers, Ref. [1] claims that a subsurface VO can facilitate water dissociation through direct and indirect pathways. The claims contradict experimental observations [2]. Using converged numbers of layers, we find that at room temperature, subsurface VOs cannot induce water dissociation on anatase TiO2 (101) [3], in agreement with experiment [2].

Ferromagnetic Weyl semimetal phase in a tetragonal structure

Vanadium-Phosphorous-Oxide β-V2OPO4 Compound Y. J. Jin1,∗, R. Wang1,2,∗, J. Z. Zhao, Z. J. Chen, Y. J. Zhao, and H. Xu1,† Department of Physics, South University of Science and Technology of China, Shenzhen 518055, P. R. China. Institute for Structure and Function & Department of physics, Chongqing University, Chongqing 400044, P. R. China. Dalian Institute of Chemical Physics,Chinese Academy of Sciences, 116023 Dalian, P. R. China and Department of Physics, South China University of Technology, Guangzhou 510640, P. R. China

Recipe for generating Weyl semimetals with extended topologically protected features

R. Wang,1,2 J. Z. Zhao,1,3 Y. J. Jin,1 W. P. Xu,1 L.-Y. Gan,1,4 X. Z. Wu,1,2 H. Xu1,*, and S. Y. Tong1,5 1Department of Physics, South University of Science and Technology of China, Shenzhen 518055, P. R. China. 2Institute for Structure and Function & Department of physics, Chongqing University, Chongqing 400044, P. R. China. 3Dalian Institute of Chemical Physics,Chinese Academy of Sciences, 116023 Dalian, P. R. China 4Key Laboratory of Advanced Technology of Materials (Ministry of Education), Superconductivity and New Energy R&D Center, Southwest Jiaotong University, Chengdu, 610031 Sichuan, P. R. China and 5School of Science and Engineering, The Chinese University of Hong Kong (Shenzhen), 518172 Shenzhen, P. R. China.

Quasi-One-Dimensional Metal-Insulator Transitions in Compound Semiconductor Surfaces.

Existing examples of Peierls-type 1D systems on surfaces involve depositing metallic overlayers on semiconducting substrates, in particular, at step edges. Here we propose a new class of Peierls system on the (101[over ¯]0) surface of metal-anion wurtzite semiconductors. When the anions are bonded to hydrogen or lithium atoms, we obtain rows of threefold coordinated metal atoms that act as one-atom-wide metallic structures. First-principles calculations show that the surface is metallic, and below a certain critical temperature the surface will condense to a semiconducting state. The idea of surface scaffolding is introduced in which the rows are constrained to move along simple up-down and/or sideways displacements, mirroring the paradigm envisioned in Peierlss description. We predict that this type of insulating state should be visible in the partially hydrogenated (101[over ¯]0) surface of many wurtzite compounds.

Nodal line fermions in magnetic oxides

We show by first-principles calculations that the Dirac nodal-line semimetal phase can co-exist with the ferromagnetic order at room temperature in chromium dioxide, a widely used material in magnetic tape applications, under small tensile hydrostatic strains. An ideally flat Dirac nodal ring close to the Fermi energy is placed in the reflection-invariant boundary of the Brillouin zone perpendicular to the magnetic order, and is topologically protected by the unitary mirror symmetry of the magnetic group

The prediction of a family group of two-dimensional node-line semimetals

D_{4h}(C_{4h})

Emergence of topological nodal loops in alkaline-earth hexaborides XB6 (X = Ca, Sr, and Ba) under pressure

, which quantizes the corresponding Berry phase into integer multiples of

The Enhancement of Surface Reactivity on CeO2 (111) Mediated by Subsurface Oxygen Vacancies

\pi

Controllable dissociation of H2O on a CeO2(111) surface

. The symmetry-dependent topological stability is demonstrated through showing that only the topologically protected nodal ring can persistently exist under small anisotropic stains preservingthe symmetry

Adsorption Induced Indirect-to-Direct Band Gap Transition in Monolayer Blue Phosphorus

D_{4h}(C_{4h})