硫在Fe(100)面吸附的第一性原理研究

基于密度泛函理论的第一性原理方法,在广义梯度近似下,计算了硫原子在Fe(100)面吸附的结构和电子性质,并计算了其分子轨道和吸附能.同时讨论了相关吸附性质与硫原子表面覆盖度(0.25～1.0ML)的关系.结果表明:硫原子吸附在H住最稳定,吸附能均随浓度的增加而单调增加;B位吸附的硫原子与Fe(100)表面的距离随浓度非单调变化,在0.5 ML时达到最大,是由较高的局域电子云重叠产生的排斥作用所导致;对比分析吸附前后硫和Fe的s及p电子的态密度,显示了硫化亚铁的生成.     

H2S在Fe(100)面吸附的第一性原理研究

基于密度泛函理论第一性原理, 在广义梯度近似下, 研究了表面覆盖度为0.25 ML (monolayer)时硫化氢分子在Fe(100)面吸附的结构和电子性质, 并与单个硫原子吸附结果进行了对比. 结果表明: 硫化氢分子吸附在B2位吸附能最小为-1.23 eV, 最稳定, B1位吸附能最大为-0.01 eV, 最不稳定; 并对硫化氢分子在B1位和B2位吸附后的电子态密度进行了分析, 也表明了吸附在B2位稳定, 且吸附在B2位后硫化氢分子几何结构变化不大; 将硫化氢中硫原子吸附与单个硫原子吸附的电子性质进行了比较, 发现前者吸附作用非常微弱; 同时对吸附后的Fe(100)面进行了对比, 单个硫原子吸附的Fe(100)面电子态密度出现了一系列峰值且离散分布, 生成了硫化亚铁, 表明在硫化氢环境下, 主要是硫化氢析出的硫原子发生了吸附. 关键词： 第一性原理 Fe(100)表面 吸附能 硫化氢     

Cs/GaN(0001)吸附体系电子结构和光学性质研究

采用基于第一性原理的密度泛函理论平面波超软赝势方法计算了 1/4ML Cs原子吸附 (2 × 2) GaN(0001) 表面的吸附能、能带结构、电子态密度、电荷布居数、功函数和光学性质. 计算发现, 1/4ML Cs 原子在 GaN(0001) 表面最稳定吸附位为 N 桥位, 吸附后表面仍呈现为金属导电特性, Cs原子吸附GaN(0001)表面后主要与表面 Ga 原子发生作用, Cs6s 态电子向最表面 Ga 原子转移, 引起表面功函数下降. 研究光学性质发现, Cs 原子吸附 GaN(0001) 表面后, 介电函数虚部、吸收谱、反射谱向低能方向移动.     

氧在Nb(110)表面吸附的第一性原理研究

通过第一性原理赝势平面波方法研究了氧在Nb(110)表面的吸附性质随覆盖度变化规律. O在Nb(110)表面最稳定吸附位是洞位,次稳定吸附位是长桥位. 在长桥位吸附时, O诱导Nb(110)表面功函数随覆盖度的增加而几乎线性增加;但当O在洞位吸附时, 与干净Nb表面相比, 覆盖度为0.75 ML和1.0 ML时功函数增加, 而覆盖度为0.25 ML和0.5 ML时功函数减小.通过对面平均电荷密度分布和偶极矩变化的讨论, 解释了由吸附导致功函数复杂变化的原因.通过对表面原子结构和态密度分析, 讨论了O在Nb表面吸附时引起表面原子结构变化以及O和Nb(110)表面原子的相互作用.     

硫在Fe(111)面吸附的密度泛函研究

采用基于密度泛函理论的第一性原理方法,系统研究了不同覆盖度下硫在Fe(111)表面的吸附构型和吸附特性,计算并分析了硫在Fe(111)表面的吸附能、电荷密度、分波态密度、电荷布局、电子局域化函数等数据.研究结果表明:S在Fe(111)面的H位吸附最稳定,并且吸附能随着覆盖度的增加而增加.另外,电子态密度、电子局域化函数和布局分析表明Fe、S之间呈较弱的共价键,这种作用力主要是Fe的3d轨道和S的3p轨道杂化所贡献,而随着覆盖度的增加,Fe、S之间的作用力逐渐减弱,这可能是由于S原子之间的排斥力减弱了Fe、S之间的作用.S在Fe(111)、Fe(110)和Fe(100)这三个晶面上吸附情况的对比分析发现,S与Fe(111)表面的相互作用最强,Fe(100)面次之,而Fe(110)面最弱.     

覆盖度对S原子在Ir(001)表面吸附性质的影响

采用第一性原理方法模拟了覆盖度对S原子在Ir(001)表面吸附能和电子结构的影响。结果表明：在覆盖度0.50 ML以下,S原子吸附在Hollow空位最稳定,且吸附能几乎不随覆盖度变化;在覆盖度0.66 ML以上吸附能随覆盖度增加而减小。吸附体系金属表面d带电子结构随覆盖度变化与O/Pt(111)吸附体系相似。这些结果与Hammer-Nørskov模型吻合。     

覆盖度对S原子在Ir(001)表面吸附性质的影响

采用第一性原理方法模拟了覆盖度对S原子在Ir(001)表面吸附能和电子结构的影响。结果表明：在覆盖度0.50 ML以下，S原子吸附在Hollow空位最稳定，且吸附能几乎不随覆盖度变化；在覆盖度0.66 ML以上吸附能随覆盖度增加而减小。吸附体系金属表面d带电子结构随覆盖度变化与O/Pt(111)吸附体系相似。这些结果与Hammer-Nørskov模型吻合。     

硫原子在镍基合金825(001)面吸附的第一性原理研究

元素硫在镍基合金表面吸附产生严重的电化学腐蚀,为从原子尺度研究硫腐蚀机理,采用第一性原理方法,构建并优化了镍基合金825的晶胞结构模型,计算分析了S原子在镍基合金825耐蚀性较差面(001)晶面的吸附及电子转移情况.结果表明:Ni原子占据顶角, Cr原子和Fe原子对称占据面心是镍基合金825稳定的晶胞结构;原子S在镍基合金825(001)面上最稳定的吸附位为四重穴位,吸附能为-6.51 eV; S吸附前后的态密度(DOS)和二维电荷差分密度图(DCD)对比发现,镍基合金825中Fe与S之间电荷偏移明显,形成离子键,易生成腐蚀产物Fe_xS_y. S的吸附对镍基合金825中Cr原子的电子分布影响不大,且合金中Cr和Ni抑制了合金中Fe与S之间的相互作用,从而提高了合金耐蚀性.     

氯原子在Cu(111)表面的吸附结构和电子态

密度泛函理论(DFT)总能计算研究了不同覆盖度下氯原子在Cu(111)表面的吸附结构和表面电子态。计算结果表明,清洁Cu(111)表面自由能 为15.72 ,表面功函数φ为4.753eV。在1/4ML和1/3ML覆盖度下,每个氯原子在Cu(111)表面fcc谷位的吸附能分别等于3.278eV/atom和3.284eV/atom。在1/2ML覆盖度下,两个紧邻氯原子分别吸附于fcc和hcp谷位,氯原子的平均吸附能为2.631eV/atom。在1/3ML覆盖度下,fcc和hcp两个位置每个氯原子吸附能的差值约为2meV/atom,与正入射X光驻波实验结合蒙特卡罗方法得到结果(<10meV/atom)基本一致。在1/4ML、1/3ML和1/2ML覆盖度下,吸附后Cu(111)表面的功函数依次为5.263eV、5.275eV和5.851eV。吸附原子和衬底价轨道杂化形成的局域表面电子态位于费米能级以下约1.2eV、3.6eV和4.5eV等处。吸附能和电子结构的计算结果表明,氯原子间的直接作用和表面铜原子紧邻氯原子数目是决定表面结构的两个重要因素。     

硫在Fe(111)面吸附的密度泛函研究

采用基于密度泛函理论的第一性原理方法,系统研究了不同覆盖度下硫在Fe（111）表面的吸附构型和吸附特性,计算并分析了硫在Fe（111）表面的吸附能、电荷密度、分波态密度、电荷布局、电子局域化函数等数据. 研究结果表明：S在Fe（111）面的H位吸附最稳定,并且吸附能随着覆盖度的增加而增加. 另外,电子态密度、电子局域化函数和布局分析表明Fe、S之间呈较弱的共价键,这种作用力主要是Fe的3d轨道和S的2p轨道杂化所贡献,而随着覆盖度的增加,Fe、S之间的作用力逐渐减弱,这可能是由于S原子之间的排斥力减弱了Fe、S之间的作用. S在Fe（111）、Fe（110）和Fe（100）这三个晶面上吸附情况的对比分析发现,S与Fe（111）表面的相互作用最强,Fe（100）面次之,而Fe（110）面最弱.     

Adsorption and decomposition of H2S on the Ge(100) surface

The adsorption and decomposition of H₂S on the Ge(100) surface is investigated. H₂S is a simple sulfur containing molecule that eventually decomposes to yield hydrogen gas and deposits sulfur on the germanium surface. The surface reactions of H₂S are investigated by ultraviolet photoelectron spectroscopy, Auger electron spectroscopy, and temperature programmed desorption. Room temperature exposure of H₂S to Ge(100) results in dissociative adsorption which can be followed easily by ultraviolet photoelectron spectroscopy. Warming the H₂S exposed surface results in some molecular desorption and further decomposition of the adsorbed species. At saturation, 0.25 ML of H₂S decomposes generating 0.5 ML of atomic hydrogen. Above the hydrogen desorption temperature some etching of the germanium surface is observed by sulfur. The etch product, GeS, is subsequently observed in temperature programmed desorption experiments. Exposure of H₂S to the Ge surface at elevated temperatures leads to higher sulfur coverages. A sulfur coverage approaching 0.5 ML can be deposited at the higher exposure temperatures.     

Adsorption of O and CO on Ir(100) from first principles

The adsorption of O and CO on Iridium (100) surface with different coverages (Θ = 1.0, 0.5, 0.25 monolayer (ML)) is studied using density functional theory (DFT). The most energetically preferred site of adsorption for O is found to be the bridge site. However, the top site is the preferred one for CO at coverages of 0.25 ML and 0.5 ML. Oxygen adsorbed on the bridge site at 0.25 ML and 0.5 ML coverages causes a row pairing. A missing row reconstruction appears in the case of 0.25 ML coverage. We find that the adsorption of O (CO) on Ir(100) surface causes disruptions of Ir–Ir bonds in the metal, which reduces (increases) the Ir–Ir bond length.     

Cu(100)表面CO分子单层膜的原子结构

利用第一性原理研究了覆盖度分别为1.00, 0.50和0.25 ML时CO分子单层膜在Cu(100)表面的吸附系统. 计算表明CO分子对不稳定. 获得了CO分子单层膜在虚拟Cu(100)表面的原子结构, 以及CO分子单层膜在Cu(100)表面吸附系统的原子结构. 当CO分子单层膜在Cu(100)表面的三个吸附位吸附, 覆盖度为1.00 ML时, 顶位和桥位都稳定, 而空心位不稳定; 覆盖度为0.50和0.25 ML时, 三个吸附位都稳定.比较吸附前后CO分子单层膜的原子结构, 可知CO分子和Cu(100)表面的相互作用强于CO分子单层膜之间的相互作用. 关键词： CO分子单层膜 自组装 CASTEP Cu(100)     

Density functional theory study of selenium adsorption on Fe(1 1 0)

The adsorption of atomic Se on a Fe(1 1 0) surface is examined using the density functional theory (DFT). Selenium is adsorbed in high-symmetry adsorption sites: the -short and long-bridge, and atop sites at 1/2, 1/4, and 1 monolayer (ML) coverages. The long bridge (LB) site is found to be the most stable, followed by the short bridge (SB) and top sites (T). The following overlayer structures were examined, p(2 × 2), c(2 × 2), and p(1 × 1), which correspond to 1/4 ML, 1/2 ML, and 1 ML respectively. Adsorption energy is −5.23 eV at 1/4 ML. Se adsorption results in surface reconstruction, being more extensive for adsorption in the long bridge site at 1/2 ML, with vertical displacements between +8.63 and −6.69% -with regard to the original Fe position-, affecting the 1st and 2nd neighbours. The largest displacement in x or y-directions was determined to be 0.011, 0.030, and 0.021 Å for atop and bridge sites. Comparisons between Se-adsorbed and pure Fe surfaces revealed reductions in the magnetic moments of surface-layer Fe atoms in the vicinity of the Se. At the long bridge site, the presence of Se causes a decrease in the surface Fe d-orbital density of states between 4 and 5 eV below Fermi level. The density of states present a contribution of Se states at −3.1 eV and −12.9 eV. stabilized after adsorption. The Fe-Fe overlap population decrease and a Fe-Se bond are formed at the expense of the metallic bond.     

Atomic oxygen adsorption on Pb(1 0 0)

We study atomic oxygen adsorption on a Pb(1 0 0) surface using density functional theory. The structures, binding energies, work function, and charge transfer of on-surface and subsurface adsorption are investigated at a range of coverages from 0.06 to 1.00 ML. The energetically favored adsorption site for on-surface adsorption is found to be a distorted hollow site for the whole coverage range studied. The distorted structures are stabilized by mixing of 6s and 6p states of lead mediated by the 2p states of oxygen. For subsurface adsorption, the sub-bridge site is found to be preferred to the sub-hollow site at low coverages, the two being nearly equal in energy at monolayer coverage. At 0.11 ML coverage, diffusion from an on-surface hollow site to a sub-bridge site is found to be barrierless, suggesting facile subsurface oxidation at low coverages. Combined on-surface and subsurface adsorption leads to the formation of a two-layer oxide structure resembling β-PbO.     

Adsorption of H<Subscript>2</Subscript>S,HS, S,and H on a stepped Fe(310) surface

Using periodic density functional theory we studied adsorption of H₂S, HS, S and H on the Fe(310) stepped surface, comparing our results with those on Fe(100). H₂S is predicted to weakly adsorb on all high-symmetry sites, with the bridge site at the step edge as preferred one, oriented perpendicularly to the (100) terraces with the two H atoms pointing out of the surface. Adsorption of HS, S, and H is more stable on the bridge, four-fold hollow, and three-fold hollow sites, respectively. The detailed analysis of the computed local density of states show common trends with the behavior of adsorption energies and is able to account for energy differences of all species adsorbed on Fe(100) and Fe(310).