Mn-Na_2WO_4/SiO_2催化剂表面活性中心结构的DFT研究

利用密度泛函方法(DFT)研究了Mn-Na2WO4/SiO2催化剂表面的活性中心结构.计算表明,在α-方石英的(111)面上,W能以单个或三个桥氧与载体作用形成稳定的四面体配位结构,Mn则能以单个桥氧与载体配位或形成不同结构的氧化物团簇;以单个桥氧担载的[WO4]四面体是最可能的甲烷活化中心.     

O3分子在CuO(110)面吸附的密度泛函理论研究

应用密度泛函理论研究了O3分子在2×1 CuO(110)面(S1)和掺杂一个Fe原子的2×1 CuO(110)面(S2)的吸附过程和电子特性. 计算结果表明, O3分子与表面S1和S2有很强的相互作用, O3分子在表面吸附反应的活化能和反应能均为负值, 反应很容易进行. 态密度和电荷密度分析结果进一步证实了O3分子在S1上吸附是桥位化学吸附, 形成表面臭氧化物, 在S2上吸附分解为1个被吸附的表面氧原子和1个自由氧分子. 电子特性分析表明, O3分子与S1和S2相互作用的本质是O3分子的价轨道2p与CuO(110)表面杂化轨道的相互作用.     

Monolayer structure of tetracene on Cu (100) surface: parallel geometry

The geometrical arrangement of tetracene on Cu (100) surface at monolayer coverage is studied by using scanning tunneling microscopy measurement and density functional theory (DFT) calculations. Tetracene molecule is found to be oriented with its molecular plane parallel to the substrate surface, and no perpendicular geometry is observed at this coverage. The molecule is aligned either in the [011] or [011] direction due to the fourfold symmetry of the Cu (100) surface. DFT calculations show that the molecule with the "flat-lying" mode has larger adsorption energy than that with the "upright standing" mode, indicating that the former is the more stable structure. With the flat-lying geometry, the carbon atoms prefer to be placed between surface Cu atoms. The molecular center prefers to be located at the bridge site between two nearest surface Cu atoms.     

Potential energy surfaces for oxygen adsorption, dissociation, and diffusion at the Pt(321) surface

We report a first-principles, periodic supercell analysis of oxygen adsorption, diffusion, and dissociation at the kinked Pt(321) surface. Binding energies and binding site preferences of isolated oxygen atoms and molecules have been determined, and we show that both atomic and molecular oxygen prefer binding in bridge sites involving coordinatively unsaturated kink Pt atoms. Binding energies of atomic and molecular oxygen in different sites correlate well with the average metallic Pt coordination number of Pt atoms forming each site, although differences exist between adsorbates in symmetrically similar sites due to the inherent chirality of the surface. Atomic O in the strongest binding bridge sites experiences relatively small energy barriers for diffusion to neighboring sites compared to O on Pt(111). However, due to the structure of the surface, O diffusion is only rapid between different sites around the kink Pt atom, whereas the effective long-range tracer diffusion, as determined from a simple course-grain model, is shown to be anisotropic and slower than on the Pt(111) surface. Four dissociation pathways for O(2) at low coverage are also reported and found to be in agreement with experimental observations of facile dissociation, even at low temperature.     

Study on the interaction between tetracene and Cu(110) surface

The electronic structure of tetracene on Cu (110) surface has been studied by using ultraviolet photoemission spectroscopy (UPS). The emission features from the organic molecule are located from 1 to 10 eV below the Fermi level, and they shift in binding energy with increasing the coverage of the organic material. For the surface with multilayer of tetracene, six well-resolved features were found at 1.90, 3.40, 4.70, 5.95, 6.95, and 9.15 eV below the Fermi level, respectively. On the surface with a lower coverage of tetracene, angle-resolved UPS measurements suggest that the molecular plane is parallel to the substrate. Density functional theory calculation confirms the flat-lying adsorption mode and shows that the tetracene molecule prefers to be adsorbed on the long bridge site with its long axis in the [110] azimuth.     

2-氯噻吩在 Rh(111) 表面吸附的密度泛函理论研究

 采用密度泛函理论探讨了 2-氯噻吩分子在 Rh(111) 表面上吸附行为. 结果表明, 平行的 hol 位及 bridge 位上的吸附最稳定. 吸附后, 2-氯噻吩键长发生明显变化, 分子平面被扭曲, 分子中 C–H(Cl, S) 相对于金属表面倾斜上翘. 垂直吸附模式不如平行吸附模式稳定, 但吸附后噻吩环未发生变形. hol 及 bridge 吸附模式下 2-氯噻吩的芳香性已遭破坏, 噻吩环上的碳原子呈现准 sp3 杂化. 在平行的 hol 位吸附后, 2-氯噻吩环累计得到 0.77 个电子, 而 Rh(111) 表面累计失去 1.19 个电子.     

Molecular assembly of rubrene on a metal/metal oxide nanotemplate

We investigated the adsorption properties and self-assembly of rubrene molecules on the copper oxide nanotemplate formed by high-temperature exposure of Cu(110) to molecular oxygen. Using high-resolution scanning tunneling microscopy under ultrahigh-vacuum conditions, we observed a complex variety of self-assembled motifs, driven by competing effects such as the chemical affinity between the organic molecule and the surface, surface coverage, and spatial confinement of the rubrene molecules within the rows of the template.     

Adsorption geometry of 4-picoline chemisorbed on the Cu(110) surface: a study of forces controlling molecular self-assembly

The adsorption of 4-picoline (4-methylpyridine) on the Cu(110) surface has been studied with time-of-flight electron stimulated desorption ion angular distribution (TOF-ESDIAD) and other methods. Using deuterium labeling in the methyl group and hydrogen labeling on the aromatic ring, it has been possible to separately monitor by TOF-ESDIAD the C-D bond directions and the C-H bond directions in the adsorbed molecule. These triangulation measurements have led to a detailed understanding of the conformation of the adsorbed molecule relative to the Cu(110) crystal lattice, allowing one to witness changes in the molecular conformation as adsorbate-adsorbate interactional effects take place for increasing coverages. At low coverages, the molecule adsorbs by the N atom at an atop Cu site with the aromatic ring parallel to the <001> azimuth and with the molecular axis inclined 33 (+/- 5) degrees along the <001> azimuth. As rows of 4-picoline molecules form long range ordered chain structures oriented along the <112> azimuth, the aromatic ring twists 29 degrees about the inclined molecular axis as a result of forces between the adsorbate molecules. The initial tilting of the molecular axis at low coverage is likely due to the interaction of the positive-outward dipole with its image in the substrate. The ring twist may result from dipoleminus signdipole forces between the adsorbate molecules in the rows formed tending to form nested parallel pyridine rings. These studies are the first to apply the TOF-ESDIAD method for the measurement of the direction of chemical bonds at more than one molecular location within an adsorbed molecule and the new method is named electron stimulated desorption-molecular triangulation (ESD-MT). The results obtained give information of importance in understanding the factors which control conformational effects during the molecular self-assembly of complex adsorbed molecules on surfaces.     

Ni(100)表面吸附SO2的密度泛函研究

以原子簇Ni14为模拟表面,采用DFT/B3LYP方法研究了二氧化硫(SO2)分子在Ni(100)表面的吸附构型、能量、电荷及态密度。结果表明,SO2分子通过S原子平铺吸附在Ni(100)的桥位最有利,计算结果与实验相符。电荷密度及态密度分析表明,Ni原子的d轨道与SO2分子的空p轨道之间存在明显的s-p作用和电荷转移,这一作用可能导致SO2分子发生解离。     

周期性密度泛函理论研究氯气在CuCl(111)表面上的吸附与解离

运用广义梯度密度泛函理论(Generalized Gradient Approximation，GGA)的PBE(Perdew-Burke-Ernzerh)方法结合周期性平板模型，研究了氯气分子和氯原子在CuCl(111)表面上的吸附。通过对不同吸附位和不同单层覆盖度下的吸附能和几何构型参数的计算和比较发现：氯气分子在CuCl(111)表面的吸附为解离吸附；单层覆盖度为0.50时的吸附构型为稳定的吸附构型；氯气分子平行吸附在CuCl(111)表面时最稳定，吸附能最大，达364.5 kJ·mol^-1；伸缩振动频率的计算结果表明，吸附后的氯气分子的伸缩振动频率与自由氯气分子的伸缩振动频率相比，都发生了红移；布居分析结果表明整个吸附体系发生了由Cu原子向氯气分子的电荷转移。氯原子吸附的计算结果显示氯原子以穴位稳定的吸附在CuCl(111)表面。     

A DFT Study of 2-Bromothiophene Adsorption on the Rh(111) Surface

<正>Adsorption behaviors of 2-bromothiophene on the Rh(111)surface were discussed with DFT.The results revealed that adsorption at the parallel hol site and bridge site was the most stable.After adsorption,bond length of 2-bromothiophene changed significantly.Molecular plane was distorted,and C-H(Br,S)in the molecule was oblique and upswept against the metal surface.Vertical adsorption site was less stable than the plane adsorption site,but there was no distortion for the thiophene ring after adsorption.Aromaticity of 2-bromothiophene was destroyed at the hol and bridge adsorption sites,and the carbon atom in the thiophene ring presented quasi-sp~3 hybridization.After adsorption at the parallel hol,2-bromothiophene obtained 0.86 electrons in total,and Rh(111)surface lost 2.08 electrons in all.     

Nanostructures’ study of chemisorptions of O2 molecule on Al (100) surface

In this study, oxygen molecule adsorption on the surface of aluminum at various positions (top, bridge, and central sites) was studied, and the binding energies of oxygen species adsorbed on aluminum were calculated using density functional theory (DFT) within the generalized gradient approximation (GGA). The potential of the adsorption of oxygen on aluminum was examined as a function of both surface coverage and adsorption site. The relative stabilities of oxygen chemisorptions were independent of both the transition metal surface and surface coverage. That is, oxygen exhibited insignificant selectivity with respect to positions on the metal surface. Our data O₂/Al surface chemisorptions revealed that the stables model for oxygen adsorption was that on the top site. The top site approach is important for the chemisorption processes because the adsorption energy for this model was lower than for the other sites. The paper presents the results of quantum chemical calculations using density functional theory method for adsorption of O₂ molecules on Al (100) surface at cubic structure with LANL2DZ, SDD and 6-31G¹ basis sets. We can extract energetic information about the stability of adsorption O₂ on aluminum surface and calculation adsorption energy.     

First-principles calculations of hydrogen diffusion on rutile TiO2(110) surfaces

Density functional calculations are performed to study the H-atom diffusion on titanium dioxide (110) surface in the cases of water-molecule dissociation and splitting of the adjacent hydroxyl OH pair. It is shown that, when a water molecule is adsorbed at a surface oxygen-vacancy site, a fragment H atom of the water molecule tends to diffuse toward the nearest-neighboring bridging-oxygen sites by using a straight-line or relay-point path. As the result, a pair of surface hydroxyl OH is formed on the same oxygen row. In a thermal process, on the other hand, such OH pair favorably splits only by using a relay-point path, i.e., by transferring one H atom from a bridging-oxygen site to a next-neighboring one along the same oxygen row by way of another in-plane oxygen site. We found that the latter splitting reaction is activated around room temperature.     

苯分子在Cu(100)面平板模型上吸附的密度泛函理论研究

使用量子化学中的密度泛函理论和平板周期模型方法，研究了苯在Cu(100)面上的吸附方式和相对稳定性. 计算结果表明，苯在Cu(100)表面的吸附属于较强的化学作用，稳定性穴位优于桥位，顶位吸附最不稳定. 在吸附过程中，C—C键有相对大的伸长，C—H键的键长变化较小，但是偏离苯环平面，并背离固体表面，顶位则是朝向表面. 吸附过程中，发生了电子从苯向铜原子的转移.     

First-principles study of the adsorption of formaldehyde on the clean and atomic oxygen covered Cu(1 1 1) surface

The interaction of formaldehyde with the clean and atomic oxygen-covered Cu(1 1 1) surfaces has been studied by means of cluster model density functional calculations in which Cu₂₂(14,8) is used to represent the perfect Cu(1 1 1) surface. The calculations point towards a η¹-H₂CO---O orientation with the oxygen atom almost on top of a copper surface atom. The formaldehyde adsorption energy is of 22–25 kJ/mol and the internal geometry of adsorbed formaldehyde is almost identical to that of the molecule in the gas-phase. The C---O bond is almost parallel to the surface and the conformation with the molecular plane normal to the surface is slightly preferred to the conformation with the molecular plane nearly parallel to the surface. A Cu₂₂---O model where atomic oxygen is adsorbed on a fcc hollow site was used to study the co-adsorption and reaction of formaldehyde with atomic oxygen. Oxygen co-adsorption has a dramatic effect on the formaldehyde adsorption energy which is increased by 50%. The calculated energy barrier for the formation of the dioxymethylene intermediate species through the H₂CO+O→H₂CO₂ reaction is of 36 kJ/mol.     

The Surface Chemistry of Water on Fe(100): A Density Functional Theory Study

The formation of water by hydrogenation of atomic oxygen is studied using density functional theory. Atomic oxygen preferentially adsorbs at the four‐fold hollow site, the hydroxyl group prefers the bridge site in a tilted configuration, and water is most stable when adsorbed at the top site with the two O? H bonds parallel to the Fe surface. Water formation by the hydrogenation of oxygen is a highly activated process on the Fe(100) surface, with similar activation energies, in the order of 1.1 eV, for the first and second hydrogen additions. A more favourable route for the addition of the second hydrogen atom involves the disproportionation of hydroxyl groups to form water and adsorbed oxygen. Dissociation of the OH is also likely since the activation energy is similar to that for disproportionation of 0.65 eV. Furthermore, the results show that the dissociation of water on Fe(100) is a non‐activated process: 0.16 eV for the zero‐coverage limit and 0.03 eV when surface oxygen is present. Herein, adsorption energies, structures and vibrational frequencies are presented for several adsorption states at 0.25 ML coverage, as well as the potential energy surface for water formation on Fe(100).     

Density function theory study of CO adsorption on Fe3O4(111) surface

Density functional theory calculations have been carried out for CO adsorption on the Fe(oct2)- and Fe(tet1)-terminated Fe(3)O(4)(111) surfaces, which are considered as active catalysts in water-gas shift reaction. It is found that the on-top configurations are most stable on these two surfaces. Some bridge configurations are also stable in which the new C-O bond formed between the surface O atom and the C atom of CO. The adsorption on the Fe(oct2)-terminated surface is more stable than on the Fe(tet1)-terminated surface. The density of state reveals the binding mechanism of CO adsorption on the two surfaces. Our calculations have also shown that the absorbed CO can migrate from the on-top site to the bridge site or 3-fold site. The oxidation of CO via surface oxygen atoms is feasible, which is in good agreement with experimental results.     

Chemisorption of HCl to the MgO(001) surface: a DFT study

We use plane wave and embedded cluster ab initio density functional calculations to study adsorption, dissociation and diffusion of the HCl molecule on the MgO(001) surface. The two methods yield comparable results for adsorption of an isolated HCl molecule and complement each other when considering charged species and coverage effects. We find dissociative chemisorption at a coverage smaller than 0.5 monolayer with a Cl(-) ion electrostatically coupled to the OH(-) ion at the surface oxygen site. The adsorption energy of the Cl(-)[dot dot dot](OH)(-) complex is 1.5 eV and the activation energy of Cl(-) diffusion away from OH(-) is 0.6 eV. There is no significant activation energy for rotation of Cl(-) around the adsorption site. At rising coverage, an increase in dipole-dipole repulsion between HCl molecules leads to a lowering of the adsorption energy per HCl and a change of binding towards hydrogen-bridge type as well as a lowering of the activation energy for Cl(-) diffusion. OH(-) formed in the surface due to HCl adsorption has a stretch frequency of 3,083 cm(-1) with Cl(-) associated and 3,648 cm(-1) with Cl(-) removed.     

Interaction of Pt clusters with the anatase TiO(2)(101) surface: a first principles study

The adsorption of Pt(n)() (n = 1-3) clusters on the defect-free anatase TiO(2)(101) surface has been studied using total energy pseudopotential calculations based on density functional theory. The defect-free anatase TiO(2)(101) surface has a stepped structure with a step width of two O-Ti bond distances in the (100) plane along the [10] direction and the edge of the step is formed by 2-fold-coordinated oxygen atoms along the [010] direction. For a single Pt adatom, three adsorption sites were found to be stable. Energetically, the Pt adatom prefers the bridge site formed by 2 2-fold-coordinated oxygen atoms with an adsorption energy of 2.84 eV. Electronic structure analysis showed that the Pt-O bonds formed upon Pt adsorption are covalent. Among six stable Pt(2) adsorption configurations examined, Pt(2) was found to energetically favor the O-O bridge sites on the step edge along [010] with the Pt-Pt bond axis perpendicular to [010]. In these configurations, one of the Pt atoms occupies the same O-O bridge site as for a single Pt adatom and the other one either binds a different 2-fold-coordinated oxygen atom on the upper step or a 5-fold-coordinated Ti atom on the lower terrace. Three triangular and three open Pt(3) structures were determined as minima for Pt(3) adsorption on the surface. Platinum trimers adsorbed in triangular structures are more stable than in open structures. In the most stable configuration, Pt(3) occupies the edge O-O site with the Pt(3) plane being upright and almost perpendicular to the [001] terrace. The preference of Pt(n)() to the coordinately unsaturated 2-fold-coordinated oxygen sites indicates that these sites may serve as nucleation centers for the growth of metal clusters on the oxide surface. The increase in clustering energy with increasing size of the adsorbed Pt clusters indicates that the growth of Pt on this surface will lead to the formation of three-dimensional particles.     

Oxidation of a two-dimensional hexagonal boron nitride monolayer: a first-principles study

Two-dimensional (2D) hexagonal boron-nitride oxide (h-BNO) is a structural analogue of graphene oxide. Motivated by recent experimental studies of graphene oxide, we have investigated the chemical oxidation of 2D h-BN sheet and the associated electronic properties of h-BNO. Particular emphasis has been placed on the most favorable site(s) for chemisorption of atomic oxygen, and on the migration barrier for an oxygen atom hopping to the top, bridge, or hollow site on the h-BN surface, as well as the most likely pathway for the dissociation of an oxygen molecule on the h-BN surface. We find that when an oxygen atom migrates on the h-BN surface, it is most likely to be over an N atom, but confined by three neighbor B atoms (forming a triangle ring). In general, chemisorption of an oxygen atom will stretch the B-N bond, and under certain conditions may even break the B-N bond. Depending on the initial location of the first chemisorbed O atom, subsequent oxidation tends to form an O domain or O chain on the h-BN sheet. The latter may lead to a synthetic strategy for the unzipping of the h-BN sheet along a zigzag direction. A better understanding of the oxidation of h-BN sheet has important implications for tailoring the properties of the h-BN sheet for applications.