共查询到18条相似文献,搜索用时 163 毫秒
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取Li_7H和Li_9H两个原子簇模拟氢原子与含台阶的金属锂表面的相互作用,以小基组用abinitio方法计算了体系的吸附和表面扩散势能面(或势能曲线),结果表明:(1)对Li_7H体系,台阶面附近沿垂直于边棱方向存在三种不同的桥位吸附位,最稳定的吸附位在上台面接近台阶边棱处,台阶面显著地改变了表面扩散活化能,台阶边棱处有一个较高的势垒,于是,迁移原子将会在台阶边棱处受到反射,并可被捕获于台阶面上及其附近,由势能面确定了最低能量表面扩散途径,(2)对Li_9H体系,在Li_7H原子簇基础上增加次表面层两个锂原子后,表面扩散活化能略有减小,氢原子在上台面的桥位吸附更趋稳定,各吸附位相对稳定性及势垒几何位置几无改变,这些结果显示了台阶面对氢原子的化学吸附和表面扩散发生扰动,台阶边棱对表面扩散起着重要作用。 相似文献
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本文用Li7(4,3)-H和Li9(5,4)-H小原子簇模拟氢原子在平坦金属锂(100)面吸附体系, 取小基组作了各吸附位吸附势能曲线及相应分子轨道能级图、吸附和表面扩散势能面的ab initio研究。结果表明, 氢原子优先吸附在配位数较高的吸附位上, 并倾向于由高配位数吸附位向低配位数吸附位迁移, 表面扩散各向异性, 扩散跳跃步长与锂单晶晶格原子间距数量级相同。从吸附和表面扩散势能确定了最低能量表面扩散途径, 分析了原子在平坦金属表面上迁移的微观过程。 相似文献
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氢在Mg_2Ni(100)面的吸附及扩散 总被引:2,自引:0,他引:2
运用第一性原理研究氢在清洁和掺杂Al的Mg2Ni(100)面的吸附及扩散.在清洁Mg2Ni(100)表面,氢原子可稳定地吸附于Mg-Ni桥位和Mg-Mg桥位,吸附能为1.19-1.52eV.在掺杂Al的Mg2Ni(100)表面,氢原子可稳定吸附于Al-Ni、Mg-Ni、Mg-Al桥位,吸附能为0.10-0.29eV.氢在掺杂Al的Mg2Ni(100)表面的吸附能低于其在清洁表面的吸附能,说明掺杂Al后氢原子与表面的相互作用减弱.过渡态计算结果表明,氢原子由清洁的Mg2Ni(100)面及掺杂Al的Mg2Ni(100)面扩散至次表层的势垒分别为0.59及-0.04eV,掺杂Al后氢原子的扩散势垒降低,说明氢原子更易由掺杂Al表面扩散至次表层.Al原子替代Mg2Ni(100)面的Mg原子减弱氢原子与表面的相互作用,降低氢原子由表层扩散至次表层的势垒,这可能是Mg2Ni合金掺杂Al可改善其吸氢动力学性能的主要原因之一. 相似文献
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本文在H-Li(100)面吸附扩散的ab initio SCF势能面基础上构造了(H_2H+H)/Li(100)面相互作用的推广LEPS势能面,并用QCT方法研究了该体系的反应动力学行为。分析势能面特征得到:H_2在Li(100)面上的吸附无需活化能,H_2在Li(100)面上的解离吸附与吸附位及吸附模式密切相关,H_2的卧式解离比立式解离要容易得多。分析各种碰撞轨迹得到:低覆盖度下双氢原子的表面复合几率很小,H_2的表面解离几率受到H_2振动量子数的控制。本文构造了一种适合于动力学研究的气体-金属表面相互作用势能面,并且,动力学QCT计算结果能够对H_2表面活化的分子束实验作出合理的解释。 相似文献
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应用原子与表面簇合物相互作用的五参数Morse势(5-MP)方法对氢原子在Ni(111)表面和次表面以及Ni(211), (533)台阶面进行了系统研究, 得到了氢原子在上述各面的吸附位、吸附几何、结合能和本征振动频率. 计算结果表明, 在Ni(111)面上, 氢原子优先吸附在三重位, 随着覆盖度的增加会吸附在次表面八面体位和四面体位. Ni(211), (533)的最优先吸附位都是四重位, 当氢原子的覆盖度增大时占据(111)平台的三重吸附位. 靠近台阶面的吸附位受台阶和平台高度的影响很大. 此外, 我们计算了氢原子在各表面的不同吸附位的扩散势垒, 获得氢原子在各表面的最低能量扩散通道. 相似文献
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构造了氮-镍相互作用的5-参数Morse势,研究了氮原子在Ni(\r\n100),Ni(110)和Ni(111)平坦表面的吸附和振动,获得了氮原子\r\n在三个低指数表面的吸附位、吸附构型、结合能和本征振动等数据,计\r\n算结果与实验结果非常吻合.同时,与Ni(100)表面对比,系统研究\r\n了氮原子在Ni(510)台阶面的吸附和扩散.计算结果表明,氮原子在\r\n台阶下部形成最稳定的吸附态,台阶对下台面上扩散的氮原子形成捕获\r\n势,对上台面上扩散的氮原子形成反射势. 相似文献
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The adsorption and dissociation of hydrogen on stepped surface (511) of nickel are studied with the embedded-atom model (EAM) method. The adsorption energy, the length of the adsorption bond and the adsorption height for a single hydrogen atom are calculated. Three kinds of stable sites are found for hydrogen adsorption. There are the double-fold bridge site B on the step edge, the three-fold hollow site H3′ on the step surface and the four-fold hollow sites H1 and H2 on the terrace surface. Compared with a hydrogen atom adsorbed on low-index (001) surface, there are two other adsorption sites near the step: the two-fold bridge site B on the step edge and the three-fold hollow site H3′ on the step surface. At the same time, the absorbability of the hydrogen atom at the site H1 is intensified. The results show that hydrogen adsorption on Ni (511) is affected by the existence of the step. The active barriers, adsorption energy and corresponding bond length for dissociation of a hydrogen molecule on the stepped surface are presented. The results show that the dissociation is easier at the bottom of the step. It is shown that the steps are the active sites for hydrogen adsorption and dissociation. 相似文献
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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. 相似文献
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Adsorption of carbon monoxide on Pd (210) and (510) stepped surfaces has been investigated by the extended London‐Eyring‐Polyani‐Sato method constructed using a five‐parameter Morse potential. Pd (210) and (510) stepped surfaces consist of terrace with (100) structure and step with (110) character. These results show that there exist common characteristics of CO adsorption on these two surfaces. At low coverage, CO adsorbs in twofold bridge site of the (100) terrace. The critical characteristics inherit that of CO molecule adsorbed in twofold bridge site of (100) original surface. When the coverage is increased, the top site of (110) step is occupied. The critical characteristics resemble that of CO molecule adsorbed in top site of (110) original surface. A number of new sites are exposed on the boundary regions, for example, the fivefold hollow site (H) of these two surfaces. There are stable adsorption sites at high coverage. Because of the different length of the (100) terrace, the (210) and (510) stepped surfaces have some different characteristics. First, CO is tilted adsorption on bridge site of terrace of (210), but perpendicular on terrace of (510) surface. Second, the bridge site (B1) where one Pd atom at the top of the step and the other at the bottom of the step is a stable adsorption site on (210), but the same type of site on Pd (510) surface is not. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Adsorption, vibration, and diffusion of O atoms on Rh low-index and (711) stepped defective surfaces
Diao ZY Hao C Wang ZX Dong CC Pang XH 《The journal of physical chemistry. B》2005,109(25):12467-12473
The adsorption, vibration, and diffusion of O atoms on Rh(100), Rh(111), Rh(110), and Rh(711) surfaces were studied using the 5-parameter Morse potential (5-MP) of interaction between an adatom and a metal surface cluster. Our theoretical calculations provide information about adsorption sites, adsorption geometry, binding energy, and eigenvibration. Our results agreed very well with experimental results. Four major results follow. First, the theoretical calculation showed that on the Rh(100) surface the 4-fold hollow site is the only adsorption site. Second, on the O-Rh(111) system, the 3-fold hollow site is the stable adsorption site. Third, on the Rh(110) surface at low coverage, the O atom is adsorbed preferably on the pseudo-3-fold site, while with increasing coverage, the O atom is adsorbed not only on the pseudo-3-fold site but also on the long bridge site. Last, as for the Rh(711) stepped surface, the 3-fold site on the (111) step is metastable, whereas the 4-fold sites on the (100) terrace are stable, which enables the O atoms to diffuse easily from the 3-fold to the 4-fold site at low coverage. Therefore, the O atoms are adsorbed preferrably on the stable 4-fold sites of the (100) terrace and then later as coverage increases on the metastable 3-fold site of the (110) step. 相似文献
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The diffusion of single n-butane and n-decane molecules on a model stepped surface, Pt655, and on a corresponding flat surface, Pt111, is investigated using molecular-dynamics simulations and anisotropic united atom model. The surface step on Pt655 causes the alkane molecules to adsorb on the lower terrace in all-trans conformations with their long molecular axes adjacent and parallel to the step edge, and to diffuse anisotropically along the surface step via a constant wiggly motion without rotation or marked deviation from the parallel adsorption configuration. At relatively high temperatures, the alkane molecules can temporarily break away from the step edge but cannot migrate across the step edge in either the downstair or upstair direction. In comparison with the diffusion on Pt111, the diffusivity of n-decane is reduced by the surface step but its diffusion barrier is hardly affected. In the case of the shorter n-butane, however, the surface step significantly reduces the diffusion energy barrier and gives rise to higher diffusion coefficients at lower temperatures. Important implications of the simulation results are discussed. 相似文献
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The microscopic diffusion processes of NO molecules on Pt(997) at low coverage were investigated using time-resolved infrared reflection absorption spectroscopy (TR-IRAS). When NO molecules adsorb on Pt(997) at low temperature, each molecule transiently migrates on the surface from the first impact point to a possible adsorption site. At 11 K, the molecules are trapped at four adsorption sites on Pt(997): the on-top sites on the (111) terrace (OT), the hollow sites on the (111) terrace (HT), the bridge sites at the step (BS) and the hollow sites at the step downstream (HS). Based on the initial population ratio for these sites, the mean lateral displacement by transient migration is estimated to be 4.1 A. By heating the surface to 45 K, the HS species migrate up to the BS sites; the migration barrier is roughly estimated to be 120 meV. In the temperature range from 70 to 77 K, TR-IRAS measurements were carried out to observe the site change of OT species to the adjacent HT sites at isothermal conditions; the activation barrier and the preexponential factor are estimated to be 200 meV and 2.0 x 10(11) s(-1), respectively. In the temperature range from 100 to 110 K, the HT species migrate across the terrace and finally reach the BS sites. The activation barrier between the HT sites and the preexponential factor are estimated to be 290 meV and 6.5 x 10(11) s(-1), respectively, from the TR-IRAS data together with kinetic Monte Carlo simulations. On the whole, the quantitative microscopic picture of NO migration on Pt(997) has been established. 相似文献
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K. Sbiaai E. Elkoraychy M. Mazroui Y. Boughaleb I. Matrane 《Surface and interface analysis : SIA》2015,47(9):855-862
A molecular‐dynamics simulation study has been performed to investigate the Cu adatom diffusion on the (110) stepped surfaces of Ag, using interatomic potentials described by the embedded atom method. We have systematically calculated the energy barriers for different possible diffusion mechanisms, which occur on the terrace and near the step edge. Our findings show that the predominant atomistic diffusion process at step edge and on the terrace is the exchange mechanism with anES barrier about 220 meV lower than that via jumping (290 meV), indicating that the incorporation of Cu adatom into Ag(110) is ‘easier’ than making a jump on the surface. On the other hand, the calculation of the Ehrlich–Schwoebel (ES) barrier demonstrates that this quantity is equal to 0 meV for the exchange process near the step edge and about 60 meV for channel–channel migration. Thus, the mass transport across steps may be important due to the lack of the ES barriers for exchange mechanism, revealing the possible layer‐by‐layer growth mode for our heterogeneous system. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献