The First-principles Calculations of H2S Adsorption and Decomposition on the ZnO（0001） Surface

The adsorption and decomposition of H2S on the ZnO(0001) surface have been investigated with first-principles calculations.The results reveal that H2S is dissociatively adsorbed on the clean ZnO(0001) surface to generate HS-and hydrogen species.To our interest,as indicated by Mulliken charge and density of states of the configuration calculation,the bonding mechanism of H2S on the ZnO(0001) surface can involve the donation of charge from the "s lone pairs" into the surface and the back donation of surface electrons to H2S.Therefore,the electrons should play an important role in decomposition.Furthermore,the reactivity of H2S adsorption and further thermal decomposition reactions on the ZnO(0001) surface have also been discussed by calculating the possible reaction pathways.As expected,H2 will be easily generated during the decomposition process.     

A DFT Study for NH3 Adsorption on the GaN （0001） Surface

1 INTRODUCTION Recently, the reaction of NH3 with III-V com- pounds[1～5] has attracted much attention, especially for the wurtzite GaN, since NH3 is the predominant raw stuff for growing crystalline GaN by both of the most important growth techniques[6～9], i.e., organo- metallic chemical vapor deposition (OMCVD) and molecular-beam epitaxy (MBE). Experimentally, Shekhar et al.[2] reported the chemisorption and reaction of hydrogen and ammonia on the single- crystalline GaN (0001…     

Structure of Oxygen and CO Adsorption on Ru(0001) Electrode

It is important to understand the chemisorption of oxygen and CO on Ru(0001) surface. CO oxidation at oxygen precovered Ru(0001) surface at low oxygen coverages gave an extremely low CO oxidation rate, and it was also observed that, with a nominal oxygen coverage exceeding ca. 3 mL, rather high CO/CO2 conversion probabilities were achieved1. In the case of coadsorption of CO and oxygen on Ru(0001) surface under UHV conditions, a model comprising two CO molecules in an (22)-O unit cel…     

Theoretical Study of N_2O Adsorption and Decomposition on the InN （0001） Surface

The adsorption and decomposition of N2O on the InN (0001) surface have been explored employing density functional theory method. To study the most favorable N2O adsorption model, ten typical adsorption cases (four for the parallel style and six for the vertical style) were proposed. The calculated results indicate that the parallel models are energetically preferred over the vertical models. The parallelly adsorbed N2O prefers to be dissociated on the surface, the dissociated O atom is combined at the fcc site, and the N-N piece is desorbed from the surface and forms N2 molecules. The comparison of the density of states of InN (0001) surface before and after N2O adsorption is analyzed in detail. Through the searching for transition state of decomposition reaction, a very low energy barrier of 45.0 KJ/mol is derived.     

Density Functional Study of the C Atom Adsorption on the α-Fe2O3 （001） Surface

The adsorption of C atoms on the α-Fe2O3(001) surface was studied based on density function theory(DFT) ,in which the exchange-correlation potential was chosen as the PBE(Perdew,Burke and Ernzerhof) generalized gradient approximation(GGA) with a plane wave basis set. Upon the optimization on different adsorption sites with coverage of 1/20 and 1/5 ML,it was found that the adsorption of C atoms on the α-Fe2O3(001) surface was chemical adsorption. The coverage can affect the adsorption behavior greatly. Under low coverage,the most stable adsorption geometry lied on the bridged site with the adsorption energy of about 3.22 eV;however,under high coverage,it located at the top site with the energy change of 8.79 eV. Strong chemical reaction has occurred between the C and O atoms at this site. The density of states and population analysis showed that the s,p orbitals of C and p orbital of O give the most contribution to the adsorption bonding. During the adsorption process,O atom shares the electrons with C,and C can only affect the outermost and subsurface layers of α-Fe2O3;the third layer can not be affected obviously.     

A Periodic Density Functional Study on Adsorption Properties of Methoxy on Au（111） Surface

1INTRODUCTION Methoxy(CH3O)has been identified as the first intermediate in the decomposition of methanol on extensive list of clean transition metal surfaces,such as Ni(100)[1],Cu(100)[2,3],Cu(111)[4],Ag(111)[5],Au(110)[6],Pd(111)[7]and Ru(0001)[8].The electronic structure of the metal is a determining factor in OH bond scission.In fact,group IB clean surfaces have shown very low activity towards this reaction,al-though there are reports on low amounts of methoxy formed on clean Cu(…     

Adsorption and Diffusion of O Atoms on Ag（210） Stepped Surface

The O-Ag(210)surface adsorption system was studied via the five-parameter Morse potential theory.Meanwhile,the 2O-Ag(210)system was investigated via the extended London-Eyring-Polanyi-Sato(LEPS)potential theory to learn the interaction between the adsorption states.Calculated results demonstrate that there are two stable on-surface adsorption sites(B and H)for O atoms on Ag(210)stepped surface.And the perpendicular vibrations are 30.3 and 42.9 meV,which are close to that observed in high resolution electron energy loss spectroscopy(HREELS).Also,there exists an octahedral subsurface adsorption state with a high vibrational frequency,and the interaction between the on-surface and subsurface O species is slight.The mode at 54.6 meV,which is close to that observed in HREELS(54-56 meV),is because of the vibration of the O atom on B site under the influence of that on H site.     

A DFT Study of Alkenes and Alkynes Reacting with H-GaN （0001） Surface

The addition reactions of alkenes and alkynes to the H-terminated GaN （0001） surface with a Ga dangling-bond have been studied employing periodic density functional theory （PDFT） calculations. Detailed information on the reaction pathways of these alkenes and alkynes with H-GaN （0001） surface is provided, which indicates that the reactions contain two steps separated by the metastable intermediates： elementary addition reaction and H-abstraction process. From the energy curves, the reactions are clearly viable in the cases of ethene, styrene and phenylacetylene; while for ethyne, the H-abstraction barrier is higher than the desorption barrier of the intermediate, so the adsorbed C2H2 in intermediate is more likely to be desorbed back into the gas phase than to form a stable adsorbed species. Furthermore, it is obvious that for either alkenes or alkynes, the systems substituted by phenyl have more stable intermediates because π conjugation could improve their stabilities.     

Adsorption Site and State of Nitrogen Atom on Ru（0001）, （1010） Low-index and （1120）, （1121） Stepped Surfaces

The adsorptions of nitrogen atoms on Ru(0001), (1010) low index surfaces and (1120), (1121) stepped surfaces were investigated by the five-parameter Morse potential(5-MP) method in details. Calculated results demonstrate that N atoms show a tendency to be adsorbed at threefold sites. No subsurface state was found for N atoms on Ru(1010) surface. There exist 6 stable adsorption sites for N atoms on Ru(1121) stepped surface which can be classified into 3 types: the on-surface adsorption state, the facet adsor...     

甲醇在Ru(0001)表面吸附的密度泛函研究

采用密度泛函理论(DFT)的B3LYP方法,以原子簇Ru15为模拟表面,对甲醇在理想的Ru(0001)面三种吸附位置(top,fcc,hcp)的吸附模型进行了几何构型优化,能量计算,Mu lliken布局分析以及振动频率计算,结果表明顶位为最有利的吸附位.这些变化与实验观察到的甲醇在过渡金属表面解离的结果相一致.同时通过对吸附过程的分析推测其可能的解离途径.     

氢原子在Ti(0001)表面吸附的密度泛函理论研究

用密度泛函理论研究了氢原子的污染对于Ti(0001)表面结构的影响. 通过PAW总能计算研究了p(1×1)、p(1×2)、3^1/2×3^1/2R30[deg]和p(2×2)等几种氢原子覆盖度下的吸附结构, 以及在上述结构下Ti(0001)面fcc格点和hcp格点的氢原子吸附. 结果表明, 在p(1×1)-H、p(1×2)-H、3^1/2×3^1/2R30[deg]-H和p(2×2)-H几种H原子覆盖度下, 以p(1×1)-H结构的单个氢原子吸附能为最大. 在p(1×1)-H吸附结构下, 由于氢原子吸附导致的Ti(0001)表面Ti原子层收缩的理论计算数值分别为-2.85%(hcp吸附)和-4.31%(fcc吸附), 因此实际上最有可能的情况是两种吸附方式都有一定的几率. 而实验中观察到的所谓“清洁”Ti(0001)表面实际上是有少量氢原子污染的表面. 不同覆盖度和氢分压下, 氢原子吸附的污染对Ti(0001)表面结构有极大的影响, 其表面的各种特性都会随覆盖度的不同而产生相应的变化.     

氢原子在Be(0001)表面吸附的密度泛函理论研究

采用第一性原理的密度泛函理论研究单个氢原子和多个氢原子在Be(0001)表面吸附性质.给出了氢吸附Be(0001)薄膜表面的原子结构、吸附能、饱和度、功函数、偶极修正等特性参数.同时也讨论了相关吸附性质与氢原子覆盖度(0.06-1.33ML)的关系.计算结果表明:氢原子的吸附位置与覆盖度之间有强烈的依赖关系,覆盖度低于0.67ML时,氢原子能量上易于占据fcc或hcp的中空位置;覆盖度为0.78ML时,中空位与桥位为氢原子的最佳吸附位;覆盖度在0.89到1.00ML时,桥位是氢原子吸附能量最有利的位置;以上覆盖度中Be(0001)表面最外层铍原子的结构均没有发生明显变化.当覆盖度为1.11-1.33ML,高覆盖度下Be(0001)表面的最外层铍原子部分发生膨胀,近邻氢原子渗入到铍表面次层,氢原子易于占据在hcp和桥位.吸附结构中的氢原子比氢分子中的原子稳定.当覆盖度大1.33ML时,计算结果没有发现相对于氢分子更稳定的吸氢结构.同时从分析偶极修正和氢原子吸附垂直高度随覆盖度的变化关系判断氢覆盖度为1.33ML时,在Be(0001)表面吸附达到饱和.     

Density Functional Theory Study for Adsorption of Oxygen and Water Molecules on 6H-SiC(0001) Surface

6H-SiC is an important semiconductor material. The 6H-SiC wafer is always exposed to a high-humidity environment and the effect from the absorbed water molecule and some relative adsorbates is not negligible. Here, the oxygen and water molecules absorbed on the 6H-SiC(0001) surface and the dissociation process were studied with density functional theory. On the 6H-SiC(0001) surface, absorbed O₂ is spontaneously dissociated into O^*, which is absorbed on a hollow site, and further transforms the 6H-SiC(0001) surface into SiO₂. The absorbed H₂O is spontaneously broken into OH^*and H^*, which are both absorbed on the top of the Si atom, and OH^* is further reversibly transformed into O^* and H^*. The H^* could saturate the dangling Si bond and change the absorption type of O^*, which could stabilize the 6H-SiC(0001) surface and prevent it from transforming into SiO₂.     

H2O在Fe3O4 (111)表面吸附的结构及热力学研究

使用密度泛函理论（GGA/PBE）对H₂O在Fe_tet1-和Fe_oct2-终结Fe₃O₄ (111)表面的吸附行为进行了研究。对于Fe_tet1-终结表面,在1/5 ML覆盖度下,带有氢键的H₂O分子以及异裂解离的结构具有最高的稳定性,而类似水合氢离子的OH₃⁺-OH结构出现在2/5 ML覆盖度下,其次为带有氢键的水的聚合体。这些结果与实验中观测到的现象一致。对于Fe_oct2-终结表面,在1/6 ML覆盖度下,分子态H₂O的吸附是有利的,而在1/3 ML覆盖度下多种吸附形式共存。H₂O吸附在Fe_tet1-终结表面比吸附在Fe_oct2-终结表面热力学上更有利。此外,通过计算局域态密度（LDOS）对吸附机理进行了分析。     

CO和H在Pt/WC(0001)表面的吸附

采用密度泛函理论(DFT)和周期平板模型,研究两种WC(0001)表面的几何结构和表面能,并对Pt原子单层(PtML)在两种WC(0001)表面的高对称性吸附位上的吸附能和分离功进行计算.结果发现,终止于W原子的WC(0001)为最稳定的WC(0001)表面,Pt原子单层以hcp位的方式吸附于W终止的WC(0001)表面是PtML/WC(0001)体系最稳定的几何构型.在此基础上研究了CO分子和H原子分别在PtML/WC(0001)表面和具有相似表面结构的Pt(111)表面的吸附行为.在0.25 ML(monolayer)低覆盖度下,与在Pt(111)表面相比,在PtML/WC(0001)表面上的Pt—C间距明显拉长和CO分子吸附能减少,说明PtML/WC(0001)表面抗CO中毒能力比Pt(111)表面高;态密度分析进一步解释了CO分子与不同表面Pt原子的成键机理.在同一覆盖度下,H原子在PtML/WC(0001)表面的最大吸附能等于甚至略高于在Pt(111)表面的,表明Pt/WC对氢气氧化反应具有良好的催化活性,是一种很有前途的质子交换膜燃料电池(PEMFC)阳极催化剂.     

氢原子在Ru(0001)表面的化学吸附

用密度泛函理论研究了氢原子的污染对于Ru(0001)表面结构的影响. 通过PAW(projector-augmented wave)总能计算研究了p(1×1)、p(1×2)、(3^(1/2)×3^(1/2))R30°和p(2×2)等几种氢原子覆盖度下的吸附结构, 以及在上述结构下Ru(0001)面fcc(面心立方)格点和hcp(六方密堆)格点的氢原子吸附. 所得结果表明, 在p(1×1)-H、p(1×2)-H、(3^(1/2)×3^(1/2))R30°-H和p(2×2)-H几种H原子覆盖度下, 以p(1×1)-H结构单个氢原子吸附能为最大. 在p(1×1)-H吸附结构下,由于氢原子吸附导致的Ru(0001) 表面第一层Ru 原子收缩的理论计算数值分别为-1.11%(hcp 吸附)和-1.55%(fcc 吸附), 因此实际上最有可能的情况是两种吸附方式都有一定的几率. 而实验中观察到的“清洁”Ru(0001)表面实际上是有少量氢原子污染的表面. 不同覆盖度和氢分压下氢原子吸附的污染对Ru(0001)表面结构有极大的影响,其表面的各种特性都会随覆盖度的不同而产生相应的变化.