Ni(111)表面一氧化碳和氢共吸附的密度泛函理论研究

本文用密度泛函理论(DFT)的总能计算研究了一氧化碳和氢原子在Ni(111)表面上p(2×2)共吸附系统的原子结构和电子态，结果表明CO和H原子分别被吸附于两个对角p(1×1)元胞的hcp和fcc位置.以氢分子和CO分子作为能量参考点，总吸附能为2.81 eV，相应的共吸附表面功函数φ为6.28 eV.计算得到的C—O，C—Ni和H—Ni的键长分别是1.19?, 1.96?和 1.71?，并且CO分子以C原子处于hcp的谷位与金属衬底原子结合.衬底Ni(111)的最外两层的晶面间距在吸附后的相对变化分别是 关键词： Fisher-Tropsch反应 催化作用 Ni(111) p(2×2)/(CO+H) 共吸附     

乙烯和乙炔基在Ni(110)表面上吸附结构的研究

采用平面波赝势方法，利用基于从头计算的软件包，对乙烯和乙炔基在Ni(110)表面上吸附的问题进行了计算. 在低覆盖度时，孤立的乙烯分子的吸附能比密集时高，乙烯分子的C-C 轴大致沿衬底的Ni原子链方向(即沿［110］晶向)，C-C轴与衬底Ni(110)表面有12°的倾斜角，乙烯分子的C—C键的键长为 0.147nm. 乙烯分子中接近顶位的C原子与衬底中距离最近的Ni原子为0.199nm. 在高覆盖度时，乙烯分子在Ni(110)表面上形成c(2×4)再构，每个表面二维元胞中有两个乙烯分子，每个乙烯分子的吸附位置与低覆盖度时相似，而C—C键长比低覆盖度时要短. 乙炔基是乙烯在Ni(110)表面上分解的产物. 关于乙炔基的计算结果表明：乙炔基的两个C原子的间距为0.131nm，比乙烯分子中C原子的间距更短. 与乙烯分子相比，乙炔基的吸附位置更靠近顶位. H原子与吸附在顶位上的C原子相连接，C—H键也大致沿衬底的Ni原子链方向，与Ni表面呈45°的倾斜角. 关键词： 乙烯和乙炔基 平面波赝势方法 吸附几何结构     

多重散射团簇方法对吸附系统SO2/Ag(110)的理论分析

利用多重散射团簇方法 (MSC)对吸附系统SO2 /Ag(110 )的S原子K边X射线吸收精细结构谱 (NEXAFS)作了理论分析 .研究表明 ,覆盖度为 0 5时 ,吸附的SO2 的S—O键长比气体状态时增长了 (0 0 14± 0 0 0 6 )nm ,OSO键角减小了 15°± 5°;SO2 分子的S原子处于芯位 ,但两个O原子处于不对称的位置 ;分子平面与 (110 )的夹角约为5 2° ,同时分子平面相对衬底表面法线有一小角度的倾斜 .MSC计算证实了该吸附系统存在一介于π 与σ 态中间的共振结构 ,这是由SO2 与衬底相互作用而诱导的     

密度泛函理论研究CO与Nin（n=1—6）团簇的相互作用

采用密度泛函理论对CO吸附在镍团簇表面进行了系统研究.结果表明,Ni_nCO团簇的最低能量结构是在Ni_n团簇最低能量结构的基础上吸附CO生长而成,CO的吸附没有改变Ni_n团簇的结构;CO分子在Ni_n团簇表面发生的是非解离性吸附,与优化的CO键长（0.1138?nm）相比,吸附后C—O键长变长（0.1180—0.1214?nm）,表明吸附后C—O键被削弱,CO分子被活化.自然键轨道分析表明,CO分子只与最近邻的Ni原子发生相互作用;CO分子与Ni原子相互作用的本质是CO分子内的杂化轨道与Ni原子3d, 4s, 4p轨道相互作用的结果. 关键词： nCO团簇')" href="#">Ni_nCO团簇 n团簇')" href="#">Ni_n团簇 平衡结构 电子性质     

CO在Pu(100)表面吸附的研究

采用密度泛函理论(DFT)研究了CO分子在Pu (100)面上的吸附. 计算结果表明：CO在Pu (100)表面的C端吸附比O端吸附更为有利,属于强化学吸附. CO吸附态的稳定性为穴位倾斜>穴位垂直>桥位>顶位. CO分子与表面Pu原子的相互作用主要源于CO分子的杂化轨道和Pu原子的杂化轨道的贡献. 穴位倾斜吸附的CO分子的离解能垒较小(0.280eV),表明在较低温度下,CO分子在Pu (100)表面会发生离解吸附,离解的C,O原子将占据能量最低的穴位. 关键词： 密度泛函理论 Pu (100) CO 分子和离解吸附     

SO2/Ni(111)吸附系统局域结构的多重散射团簇理论研究

用多重散射团族方法对SO₂/Ni(111)吸附系统的S原子ls近边X射线吸收精细结构进行了详细的计算和分析,求得吸附系统的局域结构。研究结果证实了SO₂分子在Ni(111)表面是平铺吸附的,其最佳吸附位为fcc三度芯位。吸附分子的S—O键长比气体状态时增长了(0.007±0.002)nm,分子键角∠OSO减小了10°,SO₂距衬底的吸附高度为(0.20±0.02)nm。理论计算与两组实验结果进行了直接比较。 关键词： 局域吸附结构 X射线吸收精细结构 2/Ni(111)')" href="#">吸附系统SO₂/Ni(111) 多重散射团簇方法     

多重散射团簇方法对吸附系统SO2/Ag(110)的理论分析

利用多重散射团簇方法(MSC)对吸附系统SO₂/Ag(110)的S原子K边X射线吸收精细结构谱(NEXAFS)作了理论分析.研究表明,覆盖度为0.5时,吸附的SO₂的S—O键长比气体状态时增长了(0.014±0.006)nm,OSO键角减小了15°±5°;SO₂分子的S原子处于芯位,但两个O原子处于不对称的位置;分子平面与(110)的夹角约为52°,同时分子平面相对衬底表面法线有一小角度的倾斜.MSC计算证实了该吸附系统存在一介于π^{关键词： X射线吸收精细结构 2/Ag(110)')" href="#">吸附系统SO₂/Ag(110) 多重散射团簇方法}     

CO在Pu(100)表面吸附的研究

采用密度泛函理论(DFT)研究了CO分子在Pu (100)面上的吸附. 计算结果表明：CO在Pu (100)表面的C端吸附比O端吸附更为有利，属于强化学吸附. CO吸附态的稳定性为穴位倾斜>穴位垂直>桥位>顶位. CO分子与表面Pu原子的相互作用主要源于CO分子的杂化轨道和Pu原子的杂化轨道的贡献. 穴位倾斜吸附的CO分子的离解能垒较小(0.280eV)，表明在较低温度下，CO分子在Pu (100)表面会发生离解吸附，离解的C，O原子将占据能量最低的穴位.     

c(2×2)-(K+CO)在Co{1010}表面吸附的NEXAFS研究

对CO和K共吸附在CO{1010}表面的系统进行了O的1s NEXAFS理论研究,证实吸附分子CO的键长比气体状态时增长约0.01nm.用MSC(多重散射团簇)理论计算谱与实验结果比较发现：在原π峰右侧出现了一个新的弱结构.证明了此结构是由于K通过钴衬底对CO的间接作用造成的,它具有π共振的性质. 关键词：     

第一性原理分析二氧化碳在CaO(100)表面的吸附性能

运用广义梯度密度泛函理论（GGA-PW91）结合周期平板模型方法,研究了CO2分子分别在1×1×1和2×2×1CaO(100)超晶胞面最稳定位的吸附行为。结果表明：CaO(100)表面的Osurf原子为CO2分子的有效吸附位,能够和CO2分子形成稳定吸附键C-Osurf, 其吸附能为0.858 eV。在吸附前后C和Osurf原子的价电子组态分别由2s0.892p2.47和2s1.842p4.99变化为2s0.682p2.33和2s1.902p5.17,而且在CO2分子中的O2s原子与Surface层的Casub4s原子间存在相互作用。考察了多个CO2分子在2×2×1 CaO(100)表面吸附时存在分子间相互排斥作用,发现当四个CO2分子吸附到2×2×1CaO(100)超晶胞面时,排斥能为1.76 eV,不利于CO2分子的吸附。     

Low-energy secondary emission from NiO(100)

The low-energy spectrum of secondary electrons emitted from the NiO(100) face has been investigated. The origin of the main features, at 8 and 12 eV, is discussed on the basis of their dependence on the temperature and the primary energy.     

Metastable (2S) helium atom scattering from NiO(100) and Cu(100) surfaces

The scattering of metastable 2³S He atoms (He*) from cleaved NiO(100) as well as from clean and CO-covered Cu(100) surfaces has been studied. For these varied surfaces, which were characterized in situ by ground state He atom scattering, only broad He* angular distributions without any diffraction peaks were observed. For metastable He atoms scattered from the clean Cu(100) surface a total survival probability of 1×10⁻⁶ was determined. For NiO(100) and the CO-covered Cu(100) surface values of about 1×10⁻⁵ were obtained. Time-of-flight spectra of the surviving He* atoms revealed a substantial energetic broadening which increases with the substrate temperature. This behaviour indicates a large well depth for the He*–surface interaction potential and is discussed in terms of an enhanced multiphonon excitation and/or trapping probability upon the scattering.     

LEED calculations for the NiO(100) surface

Dynamical calculations have been performed to determine the surface structure of NiO(100) from a comparison with experimental LEED data. As a preliminary to the structural determination an investigation was made of the effect of different assumptions in the construction of the muffin-tin potential. It was found that these were of secondary importance compared to the structural parameters thus giving us confidence in the final result which was that there is negligible rearrangement (<5% of the interlayer spacing) of the atoms at the NiO(100) surface.     

Analysis of the electronic structure of ultrathin NiO/Ag(100) films

Thin films of nickel oxide on a silver substrate have been extensively studied both experimentally and theoretically. In this paper we present band structure calculations of one, two, three and five layer NiO/Ag(100) systems using a GGA+U density functional method and study the approach of the system towards the bulk situation. We find that the interfacial layer is metallised and that even for a five-layer system, the substrate still affects the properties of the outermost and central layers, suggesting that these layers have not yet reached convergence towards bulk properties. This may affect some of the more sensitive properties of the system.     

Initial stages of hydrogen reduction of NiO(100)

The reduction of single crystal NiO(100) under hydrogen has been followed by AES, XPS and LEED for the pressure range of 1.0 × 10^?7 to 1.3 × 10^?6 Torr and for substrate temperatures of 150–350°C. The kinetics of reduction are controlled both by the rate of removal of lattice oxide at the surface and by the diffusion of subsurface oxygen to the oxygen-depleted surface. The rate of oxygen removal is first-order in surface oxide concentration and in hydrogen pressure. An induction period precedes the reduction reaction and its length is postulated to be controlled by surface defect concentration. The stoichiometric and reduced lattice oxygen species appear to be chemically identical and give a single symmetric XPS peak at 529.4 eV. Nickel spectra indicate a shift in XPS binding energies from those expected of the oxide to those of nickel metal early in the reduction process, although LEED indicates the NiO(100) surface lattice to remain the stable structure for surface reduced to approximately 20% of the stoichiometric oxygen concentration. Ni(100) island formation is observed, with Ni 〈010〉 and 〈001〉 directions along the NiO 〈010〉 and 〈001〉, respectively, but only after the NiO surface is severely depleted in oxygen.     

CO on NiO(100): orientation and bonding

We use thermal desorption spectroscopy to estimate the adsorption energy of CO on NiO(100) to be 7.0–8.8 kcal mol⁻¹. NEXAFS is employed to determine the orientation of the CO axis. The molecule is oriented perpendicular to the NiO(100) surface. In the present case we have resorted to angle-resolved photoelectron spectroscopy (ARUPS) to find indications that the CO molecule interacts with the surface through its carbon lone pair. The experimental analysis is in agreement with theoretical predictions that CO is held to NiO(100) mainly via electrostatic multipolar forces.     

Electron energy-loss spectroscopy of UHV-cleaved NiO (100) surfaces

Electron energy-loss spectroscopy of ～ 200 eV electrons has been applied to the study of the electronic states of clean NiO (100) surfaces. Initial attempt has been made on the identification of observed peaks, and they are attributed to the one-electronic transitions (O^2-2p → Ni²⁺3d, 4s and 4p; Ni²⁺3d → 4p, 3p → 3d and 4s), and the collective excitations (bulk plasmons of O^2-2p, Ni²⁺3d electrons, and coupled 2p and 3d electrons).     

Four-fold hollow site for S in a Ni(100) raft on NiO(100)

The reaction of H₂S with NiO(100) has been studied by polarization-dependent surface EXAFS. The results evidence reduction of the selvedge to form a Ni raft having S in four-fold sites with a S–Ni bond length of 2.21±0.02 Å. The Ni–Ni in-plane distance is 2.77±0.09 Å, representing a 6±4% contraction compared to that in NiO(100).