Ti原子在Al(110)表面吸氢过程中催化作用的第一性原理研究

运用第一性原理方法对H₂分子在Ti掺杂和纯的Al(110)表面的吸附情况进行了研究,发现有Ti原子掺杂时,存在一个H₂分子的吸附路径,即位于Al(110)面顶位Ti原子上方的H₂分子会发生解离,并与Ti原子形成TiH₂分子,然后TiH₂分子向能量更低的空位移动并接近Al(110)表面.态密度与电荷布居分析显示,吸附完成后H原子与表面Al原子存在较强的共价键作用,这为Al-H类物质及Na_{3 关键词： 钛 吸附 解离能 第一性原理}     

H2S在Cr(111)面上吸附与解离的第一性原理研究

采用了第一性原理研究了H₂S在Cr(111)面的吸附解离过程，利用吸附能、吸附构型和偏态密度图(PDOS)研究了H₂S及其解离产物在Cr(111)面上的吸附情况，都偏向倾斜吸附在Cr(111)面.同时研究了HS/H和S/H共吸附情况，得到共吸附物质在Cr(111)面上有明显的相互作用.最后使用线性同步和二次同步变换方法确定了解离反应的过渡态，了解到第一、二步解离的活化能分别为1.65 eV、0.82 eV,H₂S分子在Cr(111)面上的解离过程是放热反应，反应能为-2.90 eV.     

腐蚀介质在γ-Fe (111)表面吸附的第一性原理研究

氯化物熔盐作为传热储热工质，在太阳能热发电系统中应用时会造成金属管道的腐蚀和失效，严重威胁系统的运行安全.本文采用第一性原理方法，构建了不同腐蚀介质(Cl原子、H原子、O原子、OH基团以及H₂O分子)在γ-Fe(111)表面的吸附微观物理模型，并阐明了其吸附性能.结果发现：Cl原子和H原子在γ-Fe(111)表面最稳定的吸附点位为Fcc位，O原子和OH基团最稳定的吸附位点为Hcp位，H₂O分子最稳定的吸附位点位Top位.另外，O原子在γ-Fe(111)表面的吸附能和得到的电荷数最大，分别为-8.073 eV和0.53.这为管道的腐蚀研究提供了理论支撑.     

Ag(111)和Au(111)上铋的初始生长行为

半金属铋(Bi)的表面合金具有的Rashba效应,和其具体结构性质有重要关联.本文结合扫描隧道显微镜(STM)和密度泛函理论(DFT),系统地研究了Bi原子在Ag(111)和Au(111)上的不同初始生长行为.在室温Ag(111)上,连续的Ag₂Bi合金薄膜会优先在Ag台阶边缘形成;在570 K Ag(111)上,随着覆盖度增加到0.33分子层(ML),Bi优先取代配位数低的台阶边原子并从单原子随机分布转变为长程有序的Ag₂Bi合金相;随着覆盖度增加,Ag₂Bi通过退合金过程转变成p×3^1/2结构的Bi膜.Bi在室温和570 K的Au(111)上的生长行为一致:在覆盖度低于0.40 ML时,Bi会优先吸附在配位为5的Au原子上,并以单原子和团簇的形式分别分散在Au(111)的密堆积区域和鱼骨纹重构的拐角处;随着覆盖度增加到0.60 ML,无序的Bi会逐渐转变成长程有序的((37)^1/2×(37)^1/2)相;Bi的吸附会导致Au(111)表面应力逐步释放.Bi在Ag(111)和Au(111)上的不同生长行为表明,Bi原子与衬底之间的相互作用起着关键作用.     

过渡族金属掺杂Al(111)表面对氢分子催化分解的影响

为了探求过渡金属催化剂对催化合成储氢材料NaAlH₄效果的影响, 本文采用第一性原理方法研究了多种金属原子取代Al (111)表面铝原子形成的合金表面对氢的催化分解的影响. 计算结果表明, Sc, V, Fe, Ti原子掺杂的表面对氢分子分解具有催化作用. H₂在对应的掺杂表面催化分解所需要的活化能分别为0.54 eV, 0.29 eV, 0.51 eV, 0.12 eV. H原子在Sc, V, Ti掺杂表面扩散需要的活化能分别为0.51 eV, 0.66 eV, 0.57 eV. 同时, 过渡金属掺杂在Al表面时倾向于分散分布, 增加掺杂表面的掺杂原子个数, 掺杂表面的催化效果体现为单个掺杂过渡金属原子的催化效果. 本研究将为金属掺杂Al (111)表面催化加氢合成NaAlH₄提供理论参考.     

小分子在Pd(100)面上的共吸附

本文应用紧束缚模型和单电子理论研究了几种小分子在Pd(100)面上的共吸附特性,结果表明:在Pd(100)面上两个吸附分子(或吸附原子)间的间接相互作用随吸附质与衬底之间的耦合强度的减小呈现振荡性衰减的趋势,并且,当O₂或H₂存在时,NO在Pd(100)面上的解离将受到影响,此外,根据两吸附质之间的间接相互作用,推断出一些吸附层结构,这些结果与实验结果作了比较。 关键词：     

吸附Al,Sn后Si(111)面的电子结构及其比较

通过对吸附原子和衬底Si原子由于相互作用而产生的轨道交叠占有几率(OOP)和集团态密度的分析发现吸附Al和吸附Sn的Si(111)面能带中电子的占据状态很不一样,Si(111)3^1/2×3^1/2-Sn中有一个半充满的表面带,从而使体系具有表面金属性。而Si(111)3^1/2×3^1/2-Al中电子填满吸附原子和表面Si原子成键的表面态,反键的表面态全空,因此吸Al后的Si(111)面可能出现半导体特性。计算结果与实验结果 关键词：     

H2O分子在Fe(100), Fe(110), Fe(111)表面吸附的第一性原理研究

采用第一性原理研究了H2O分子在Fe(100),Fe(110),Fe(111)三个高对称晶面上的表面吸附.结果表明,H2O分子在三个晶面上的最稳定结构皆为平行于基底表面的顶位吸附结构.H2O分子与三个晶面相互作用的吸附能及几何结构计算结果表明H2O分子与三个晶面的相互作用程度不同,H2O分子与Fe(111)晶面的相互作用最强,其次是Fe(100),相互作用最弱的是Fe(110)表面,而这与晶面原子的排列密度相关.吸附体系的电子结构计算结果也得出了相似的结论.同时电荷布居分析表明,H2O分子与Fe表面相互作用时,O原子与基底原子之间的电荷交换使基底Fe原子表面带负电,导致表面电位降低,也促使Fe表面更易于发生电化学腐蚀反应.     

H2O分子在Fe（100）, Fe（110）, Fe（111）表面吸附的第一性原理研究

采用第一性原理研究了H₂O分子在Fe（100）,Fe（110）,Fe（111）三个高对称晶面上的表面吸附.结果表明,H₂O分子在三个晶面上的最稳定结构皆为平行于基底表面的顶位吸附结构.H₂O分子与三个晶面相互作用的吸附能及几何结构计算结果表明H₂O分子与三个晶面的相互作用程度不同,H₂O分子与Fe（111）晶面的相互作用最强,其次是Fe（100）,相互作用最弱的是Fe（110）表面,而这与晶面原子 关键词： 第一性原理 Fe单晶表面 2O分子')" href="#">H₂O分子 分子吸附     

Ni与钇稳定的氧化锆(111)表面相互作用以及界面活性的第一性原理研究

采用基于密度泛函理论的第一性原理方法, 系统研究了Ni原子在钇稳定的氧化锆(YSZ)(111)和富氧的YSZ(YSZ+O)(111)表面不同位置的吸附, 以及CO和O₂分子在Ni₁(单个镍原子)/YSZ和Ni₁/YSZ+O表面吸附的几何与电子结构特征. 结果表明: 1) 单个Ni原子倾向于吸附在O原子周围, 几乎不吸附在Y原子周围, 且Ni原子在氧空位上吸附最稳定; 2)和YSZ相比, 单个Ni原子在YSZ+O表面易发生氧化现象, Ni原子失去1.06 e电子, 被氧化成了Ni⁺, 吸附能力更强; 3)被氧化的Ni催化活性大幅下降, 大大减弱了表面对O₂和CO等燃料气体的吸附作用.     

Adsorption of H2O on Al(111)

The adsorption of H₂O on Al(111) has been studied by ESDIAD (electron stimulated desorption ion angular distributions), LEED (low energy electron diffraction), AES (Auger electron spectroscopy) and thermal desorption in the temperature range 80–700 K. At 80 K, H₂O is adsorbed predominantly in molecular form, and the ESDIAD patterns indicate that bonding occurs through the O atom, with the molecular axis tilted away from the surface normal. Some of the H₂O adsorbed at 80 K on clean Al(111) can be desorbed in molecular form, but a considerable fraction dissociates upon heating into OH_ads and hydrogen, which leaves the surface as H₂. Following adsorption of H₂O onto oxygen-precovered Al(111), additional OH_ads is formed upon heating (perhaps via a hydrogen abstraction reaction), and H₂ desorbs at temperatures considerably higher than that seen for H₂O on clean Al(111). The general behavior of H₂O adsorption on clean and oxygen-precovered Al(111) (θ_O ? monolayer) is rather similar at low temperature, but much higher reactivity for dissociative adsorption of H₂O to form OH _adsis noted on the oxygen-dosed surface around room temperature.     

Methanol decomposition on platinum (111)

The interaction of methanol with clean and oxygen-covered Pt(111) surfaces has been examined with high resolution electron loss spectroscopy (EELS) and thermal desorption spectroscopy (TDS). On the clean Pt(111) surface, methanol dehydrogenated above 140 K to form adsorbed carbon monoxide and hydrogen. On a Pt(111)-p(2 × 2)O surface, methanol formed a methoxy species (CH₃O) and adsorbed water. The methoxy species was unstable above 170 K and decomposed to form adsorbed CO and hydrogen. Above room temperature, hydrogen and carbon monoxide desorbed near 360 and 470 K, respectively. The instability of methanol and methoxy groups on the Pt surface is in agreement with the dehydrogenation reaction observed on W, Ru, Pd and Ni surfaces at low pressures. This is in contrast with the higher stability of methoxy groups on silver and copper surfaces, where decomposition to formaldehyde and hydrogen occurs. The hypothesis is proposed that metals with low heats of adsorption of CO and H₂ (Ag, Cu) may selectively form formaldehyde via the methoxy intermediate, whereas other metals with high CO and H₂ chemisorption heats rapidly dehydrogenate methoxy species below room temperature.     

H2O在Al(111)表面吸附的量子化学研究

用量子化学从头算方法,以原子族Ａｌ１０模拟表面,研究了水在Ａｌ（１１１）表面上不同吸附拉的吸附情况,计算得到了稳定的吸附构型和结合能,结果表明：顶位是其最佳吸附位,而且水在表面能以两种取向被吸附,距表面较远时,Ｈ端靠近表面,然后跨过一能垒到达最佳吸附位,此时氧端靠近表面。在吸附过程中,水向表面转移电荷,导致表面功函降低,在氧原子不加极化函数进,水分子的二次轴垂直于表面时能量最低;当考虑中氧的ｄ轨道     

Ar adsorptions on Al (111) and Ir (111) surfaces: a first-principles study

We investigate the adsorptions of Ar on Al (111) and Ir (111) surfaces at the four high symmetry sites, i.e., top, bridge, fcc- and hcp-hollow sites at the coverage of 0.25 monolayer (ML) using the density functional theory within the generalized gradient approximation of Perdew, Burke and Ernzerhof functions. The geometric structures, the binding energies, the electronic properties of argon atoms adsorbed on Al (111) and Ir (111) surfaces, the difference in electron density between on the Al (111) surface and on the Ir (111) surface and the total density of states are calculated. Our studies indicate that the most stable adsorption site of Ar on the Al (111) surface is found to be the fcc-hollow site for the (2 × 2) structure. The corresponding binding energy of an argon atom at this site is 0.538 eV/Ar atom at a coverage of 0.25 ML. For the Ar adsorption on Ir (111) surface at the same coverage, the most favourable site is the hcp-hollow site, with a corresponding binding energy of 0.493 eV. The total density of states (TDOS) is analysed for Ar adsorption on Al (111) surface and it is concluded that the adsorption behaviour is dominated by the interaction between 3s, 3p orbits of Ar atom and the 3p orbit of the base Al metal and the formation of sp hybrid orbital. For Ar adsorption on Ir (111) surface, the conclusion is that the main interaction in the process of Ar adsorption on Ir (111) surface comes from the 3s and 3p orbits of argon atom and 5d orbit of Ir atom.     

Vibration spectroscopy of benzene adsorbed on Pt(111) and Ni(111)

High resolution electron energy loss spectroscopy has been applied to study the adsorption of benzene (C₆H₆ and C₆D₆) on Pt(111) and Ni(111) single crystal surfaces between 140 and 320 K. The vibrational spectra provide evidence that benzene is chemisorbed with its ring parallel to the surface, predominantly π bonded to the platinum and nickel surface respectively. A significant frequency increase of the CH-out-of-plane bending mode, largest in the case of platinum, is observed compared to the free molecule. On both metals two phases of benzene exist simultaneously, characterized by a different frequency shift. The shifts are explained by electronic interaction between the metal d-orbitals and molecules adsorbed in on top and threefold hollow sites respectively. The vibrational spectra of the multilayer condensed phase of benzene exhibit the infrared active modes of the gasphase molecule as expected.     

Low-energy electron diffraction,Auger electron spectroscopy,and thermal desorption studies of chemisorbed CO and O2 on the (111) and stepped [6(111) × (100)] iridium surfaces

The adsorption of CO, O₂, and H₂O was studied on both the (111) and [6(111) × (100)] crystal faces of iridium. The techniques used were LEED, AES, and thermal desorption. Marked differences were found in surface structures and heats of adsorption on these crystal faces. Oxygen is adsorbed in a single bonding state on the (111) face. On the stepped iridium surface an additional bonding state with a higher heat of adsorption was detected which can be attributed to oxygen adsorbed at steps. On both (111) and stepped iridium crystal faces the adsorption of oxygen at room temperature produced a (2 × 1) surface structure. Two surface structures were found for CO adsorbed on Ir(111); a (√3 × √3)R30° at an exposure of 1.5–2.5 L and a (2√3 × 2√3)R30° at higher coverage. No indication for ordering of adsorbed CO was found on the Ir(S)-[6(111) × (100)] surface. No significant differences in thermal desorption spectra of CO were found on these two faces. H₂O is not adsorbed at 300 K on either iridium crystal face. The reaction of CO with O₂ was studied on Ir(111) and the results are discussed. The influence of steps on the adsorption behaviour of CO and O₂ on iridium and the correlation with the results found previously on the same platinum crystal faces are discussed.     

First-principles study of dissociation processes of O2 molecular on the Al (111) surface

The trajectories of adsorption and dissociation process of O₂ on the Al (111) surface were studied by the spin-polarized ab initio molecular dynamics method, and the adsorption activation energy was clarified by the NEB method with hybrid functionals. Three typical dissociation trajectories were found through simulation of O₂ molecule at different initial positions. When vertically approaches to the Al surface, the O₂ molecule tends to rotate, and the activation energy is 0.66eV. If O₂ molecule does not rotate, the activation energy will increase to 1.43 eV, and it makes the O atom enter the Al sublayer eventually. When the O₂ molecules parallel approach to the Al surface, there is no activation energy, due to the huge energy released during the adsorption process.     

Benzene adsorption on nickel (100) and (111) faces studied by leed and high resolution electron energy loss spectroscopy

Studies of benzene (C₆H₆ and C₆D₆) adsorption have been performed by high resolution electron energy loss spectroscopy (HRELS) and LEED experiments on nickel (100) and (111) single crystal faces at room temperature. Chemisorption induces ordered structures, c(4 × 4) on Ni(100) and (2√3 × 2√3)R30° on Ni(111), and typical energy loss spectra with 4 loss peaks accurately identified with the strongest infrared vibration bands of the gazeous molecules. Benzene chemisorption preserves the aromatic character of the molecule and involves respectively 8 nickel surface atoms on the (100) face and 12 on the (111) face by adsorbed molecule. The interaction takes place via the π electrons of the ring. Significant shifts of the CHτ bending and CH stretching vibrations show a weakening of the CH bonds due to the formation of the chemisorption bond and a coupling of H atoms with the nickel substrate.     

The mechanism of H2 dissociation and adsorption on Mn-modified Ni(111) surface: A density functional theory-based investigation

The mechanism of H₂ dissociative adsorption on Mn-modified Ni(111) surface is investigated and explained using spin-polarized density functional theory (DFT). Potential energy surface (PES) is used to determine the efficient reaction pathway of H₂ on the surface. The dissociative adsorption of H₂ in the hollow sites with its center-of-mass (CM) positioned on top of Ni atom has low activation barrier. This is lower compared if its CM is on top of the Mn atom. The difference in the reactivity of H₂ with Ni and Mn as the CM is corroborated by the positions of the bonding and antibonding orbitals of H₂ as it approaches the surface which is verified from local density of states (LDOS). The greater density of states in the region around the Fermi level of the d_zz, d_xz, and d_yz orbitals of the Ni atom explains the low activation barrier obtained for the dissociation of H₂ on top of the Ni atom in the Mn-modified Ni(111) surface.     

Electronic structures of chemisorption systems on Si(111) surface I. Si(111)7 × 7/H,Cl

Electronic structures of chemisorption on Si(111)/H,C1 are investigated by the first principle DV-Xα cluster method. The calculations are carried out for chemisorption on different sites, based on the Si₁₃H₁₅ cluster, and the effect of surface vacancy and buckling on the electronic structure is examined in detail. The present calculation shows that the Si₁₃H₁₅ surface cluster reproduces very well the more sophisticated band calculation for the Si(111) surface. It is concluded that the vacancy model with chemisorbed atoms at appropriate sites is reasonable to interpret the observed UPS of Si(111) 7 × 7/H,C1. The charge transfer between the substrate atom and the adatom depends strongly both on the chemisorption sites and on the electronegativitv difference.