Theoretical study of NO adsorption on gold surfaces

The activities of neutral,anionic,and cationic Au(111),Au(100),and Au(310) surfaces,as well as an Au adatom on Au(111) surface towards NO adsorption have been studied by performing density functional theory calculations.It was found that the activity of gold increases as the coordination number of the gold atoms decreases,and that the cationic surfaces are generally more active than the neutral and anionic surfaces.The activity of Au surfaces towards NO adsorption is attributable to the presence of low coor...     

Effects of coverage and solvent on H2S adsorption on the Cu(100) surface: A DFT study

Density functional theory is used to investigate the effects of coverage and solvent on the adsorption of H₂S on the Cu(100) surface. In this work, the adsorption energies, structural parameters and Mulliken charges of the adsorbed H₂S are calculated. The results show that when the coverage of H₂S is high (1 ML), H₂S molecule cannot adsorb on the Cu(100) surface spontaneously, and the decomposition of H₂S preferentially occurs at the bridge site. When the coverage decreases to 1/4 ML coverage, H₂S molecule does not exhibit the decomposition, but bonds to the top Cu atom with the tilted adsorption. Furthermore, when the coverage is 1/9, 1/16 and 1/25 ML, H₂S adsorption remains stable. In addition, the stability of H₂S adsorption on the Cu(100) surface improves rapidly when the solvent dielectric constant (ε) increases from 1 to 12.3 corresponding to the vacuum and pyridine, respectively. For the higher ε (≥24.3), the effect of the solvent on the H₂S adsorption was greatly reduced. In this work, both coverage and solvent are shown to have an important effect on the H₂S adsorption on the Cu(100) surface, which might be useful to improve the future similar simulations. Copyright © 2015 John Wiley & Sons, Ltd.     

CO2在Fe3O4(111)表面的吸附结构及能量研究

利用密度泛函理论研究了CO₂在Fe₃O₄（111）表面Fe_tet1和Fe_oct2两种终结的吸附行为。在Fe_tet1终结表面,当覆盖度为1/5 ML时,CO₂倾向于线性吸附;而在高覆盖度下,弯曲的CO₂与表面O作用形成CO₃^2-结构。在Fe_oct2终结表面,CO₂倾向于弯曲吸附,在1/6 ML和1/3 ML覆盖度时都可以形成CO₃^2-和-COO结构。覆盖度对Fe_tet1终结的表面影响很弱,但是对Fe_oct2终结的表面影响很大。从热力学上来说,CO₂在Fe_oct2终结表面的吸附要比Fe_tet1终结表面更有利。     

Study of CO adsorption on perfect and defective pyrite(100)surfaces by density functional theory

First-principles calculations based on density functional theory (DFT) and the generalized gradient approximation (GGA) have been used to study the adsorption of CO molecule on the perfect and defective FeS 2 (100) surfaces. The defective Fe 2 S(100) surfaces are caused by sulfur deficiencies. Slab geometry and periodic boundary conditions are employed with partial relaxations of atom positions in calculations. Two molecular orientations, Cand O-down, at various distinct sites have been considered. Total energy calculations indicated that no matter on perfect or deficient surfaces, the Fe position is relatively more favored than the S site with the predicted binding energies of 120.8 kJ/mol and 140.8 kJ/mol, respectively. Moreover, CO was found to be bound to Fe atom in vertical configuration. The analysis of density of states and vibrational frequencies before and after adsorption showed clear changes of the C–O bond.     

First-principles characterization of formate and carboxyl adsorption on stoichiometric CeO2(111) and CeO2(110) surfaces

Molecular adsorption of formate and carboxyl on stoichiometric CeO₂(111) and CeO₂(110) surfaces was studied using periodic density functional theory (DFT+U) calculations. Two distinguishable adsorption modes (strong and weak) of formate are identified. The bidentate configuration is more stable than the monodentate adsorption configuration. Both formate and carboxyl bind at the more open CeO₂(110) surface are stronger. The calculated vibrational frequencies of two adsorbed species are consistent with the experimental measurements. Finally, the effects of U parameters on the adsorption of formate and carboxyl over both CeO₂ surfaces were investigated. We found that the geometrical configurations of two adsorbed species are not affected by different U parameters (U = 0, 5, and 7). However, the calculated adsorption energy of carboxyl pronouncedly increases with the U value while the adsorption energy of formate only slightly changes (<0.2 eV). The Bader charge analysis shows the opposite charge transfer occurs for formate and carboxyl adsorption where the adsorbed formate is negatively charge while the adsorbed carboxyl is positively charged. Interestingly, with the increasing U parameter, the amount of charge is also increased.     

Pt adsorption on the PbTiO3(110) polar surface: a density functional theory study

The monolayer (ML) and submonolayer Pt on both terminations of PbTiO₃(110) polar surface have been studied by using density functional theory (DFT) with projector‐augmented wave(PAW) potential and a supercell approach. The most favored ML Pt arrangements on PbTiO and O₂ terminations are the hollow site and the short‐bridge site, respectively. By examining the geometries of different ML arrangements, we know that the dominant impetus for stability of the favored adsorption site for PbTiO termination is the Pt–Ti interaction (mainly from covalent bonding), while that for O₂ termination is the Pt–O interaction (mainly from ionic bonding). In addition, the appearance of the gap electronic states in the outermost layers of each termination indicates that a channel for charge transfer between adsorbed layer and substrate is formed. Moreover, the interface hybridization between Pt 5d and O 2p orbitals is also observed, especially for ML Pt on O₂ termination. The stability sequences for various arrangements of 1/2 ML Pt adsorption conform well with those of ML Pt adsorption, and the most stable arrangement is energetically more favorable than the corresponding ML coverage in the view of adsorption energy maximization. The behavior, i.e. the increase in adsorption energy with decrease in coverage, indicates that Pt? Pt interactions weaken those between Pt and the substrate. Copyright © 2009 John Wiley & Sons, Ltd.     

A DFT study of the adsorption and dissociation of CO on Fe(100): influence of surface coverage on the nature of accessible adsorption states.

In the present article, we report adsorption energies, structures, and vibrational frequencies of CO on Fe(100) for several adsorption states and at three surface coverages. We have performed a full analysis of the vibrational frequencies of CO, thus determining what structures are stable adsorption states and characterizing the transition-state structure for CO dissociation. We have calculated the activation energy of dissociation of CO at 0.25 ML (ML = monolayers) as well as at 0.5 ML; we have studied the dissociation at 0.5 ML to quantify the destabilization effect on the CO(alpha3) molecules when a neighboring CO molecule dissociates. In addition, it is shown that the number and nature of likely adsorption states is coverage dependent. Evidence is presented that shows that the CO molecule adsorbs on Fe(100) at fourfold hollow sites with the molecular axis tilted away from the surface normal by 51.0 degrees. The asorprton energy of the CO molecule is -2.54 eV and the C-O stretching frequency is 1156 cm(-1). This adsorption state corresponds to the alpha3 molecular desorption state reported in temperature programmed desorption (TPD) experiments. However, the activation energy of dissociation of CO(alpha3) molecules at 0.25 ML is only 1.11 eV (approximately 25.60 kcal mol(-1)) and the gain in energy is -1.17 eV; thus, the dissociation of CO is largely favored at low coverages. The activation energy of dissociation of CO at 0.5 ML is 1.18 eV (approximately 27.21 kcal mol(-1)), very similar to that calculated at 0.25 ML. However, the dissociation reaction at 0.5 ML is slightly endothermic, with a total change in energy of 0.10 eV Consequently, molecular adsorption is stabilized with respect to CO dissociation when the CO coverage is increased from 0.25 to 0.5 ML.     

First-principles study on the effect of arsenic impurity on oxidation of pyrite surfaces

Arsenic (As) frequently exists in pyrite (FeS₂) in the form of impurities. The oxidation behavior of As in FeS₂ is important in environmental science, mineral processing, and other related fields. The adsorption behaviors of H₂O and O₂ molecules on the As-bearing pyrite (100) surface (As FeS₂(100)) are studied using the density functional theory (DFT). The results show that As prefers the S site on the pyrite (100) surface (FeS₂(100)). In the absence of O₂, an isolated H₂O molecule does not dissociate when adsorbed at an iron (Fe) site and is repelled at an As site. Furthermore, the surface area around the As atoms exhibits a hydrophobic behavior. Adsorption energy analysis reveals that the presence of As atoms is unfavorable for the adsorption of H₂O molecules on the pure FeS₂ surface, and that the adsorption of H₂O molecules on the As FeS₂(100) is physical adsorption. In the absence of H₂O, it is suggested that the O₂ molecule easily dissociates on both the pure FeS₂(100) and As FeS₂(100). The adsorption of O₂ on the As-bearing surface is weaker than that on the pure FeS₂(100). For the co-adsorption of H₂O and O₂, the adsorption energy on the As-bearing surface is more negative than that on the pure surface. This indicates that the presence of As promotes surface oxidation. Additionally, two  OH and O (AsO or SO) or  O (Fe O) species are formed on the surface of pyrite when the H₂O molecule is dissociated.     

基于密度泛函理论计算的CO2在SrTiO3(100)表面的吸附

通过密度泛函理论的第一性原理,模拟了CO2分子在SrTiO3(100)表面TiO2-和SrO-位点上的吸附行为,获得了CO2在几种不同吸附模型下的结构参数及表面吸附能,进而研究了吸附机理和结构稳定性.计算结果表明,当CO2的C原子吸附在SrTiO3(100)表面SrO-及TiO2-位点的氧原子上时,吸附结构较稳定,尤其是C、O原子共吸附在TiO2-位点时最稳定,而其余吸附模型则不稳定.对吸附稳定模型的Mulliken布局数及态密度分析显示:CO2分子在SrTiO3(100)表面吸附主要是由于SrTiO3(100)面的电子跃迁至CO2分子,CO2分子得到电子形成弯曲的CO2-阴离子结构,并伴随着C-O键的伸长,从而达到吸附活化CO2的目的.     

The influence of promoters and poisons on carbon monoxide adsorption on Rh(100): a DFT study.

Density functional theory calculations were performed to determine the pairwise lateral interaction energies between carbon monoxide and coadsorbed elements from the first three rows of the periodic table on a Rh(100) surface. The atoms were placed in a c(2x2) arrangement of fourfold hollow sites and the carbon monoxide probe molecule in a p(2x2) arrangement, so that each CO molecule had four atoms as nearest neighbours. The alkali atoms show an attractive interaction with CO while the other atoms show a repulsive interaction. For second-row elements the maximum repulsion is at nitrogen and for third-row elements at sulphur. Attempts to correlate the interaction energies with properties of the system, such as electronegativity, distances, or change in work function, failed, which implies that each combination of adsorbates needs to be calculated separately.     

Fe元素及点缺陷对焦炭表面NH_3异相吸附的影响:密度泛函理论研究

采用密度泛函理论,并使用具有周期性边界条件的石墨烯模型近似模拟焦炭表面,研究了Fe原子修饰及点缺陷对NH_3在焦炭表面异相吸附的影响。计算结果表明,NH_3分子在点缺陷石墨烯表面的吸附属于物理吸附,结合能为-0.381 e V;NH_3分子吸附在Fe修饰的完整石墨烯表面属于化学吸附,吸附能为-1.442 eV; Fe原子修饰及点缺陷单独存在下NH_3的吸附能均大于NH_3在完整石墨烯表面的吸附(吸附能为-0.190 eV)。此外,Fe原子修饰与点缺陷共存对NH_3的吸附具有协同作用,结合能达到-3.538 eV,明显大于两者单独存在下NH_3的吸附能之和,综合分析Mulliken布居数与态密度,Fe原子与石墨烯表面、NH_3分子之间有更多地电荷转移,可以解释两者共存对NH_3吸附协同促进的原因。     

甲氧基在Rh(111)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Rh13(9,4)为模拟表面,在6-31G(d,p)与Lanl2dz基组水平上,对甲氧基在Rh(111)表面的四种吸附位置(fcc、hcp、top、bridge)的吸附模型进行了几何优化、能量计算、Mulliken电荷布局分析以及前线轨道的计算。结果表明,当甲氧基通过氧与金属表面相互作用时,在bridge位的吸附能最大,吸附体系最稳定,在top位转移的电子数最多;吸附于Rh(111)面的过程中C—O键被活化,C—O键的振动频率发生红移。     

HCN Adsorption on the Fe(100), Fe(111) and Fe(110) Surfaces: a Density Functional Theory Study

Twenty kinds of adsorptions of HCN on the Fe(100), Fe(111) and Fe(110) surfaces at the 1/4 monolayer coverage are found using the density functional theory. For Fe(100), the adsorption energy of the most stable configuration where the HCN locates at the fourfold site with the C-N bonded to four Fe atoms is 1.928 eV. The most favored adsorption structure for HCN on Fe(111) is f-η3(N)-h-η3(C), in which the C-N bond is almost parallel to the surface, and the adsorption energy is 1.347 eV. On Fe(110), the adsorption energy in the most stable configuration in which HCN locates at the two long-bridge sites is 1.777 eV. The adsorption energy of the parallel orientation for HCN is larger than that of the perpendicular configuration. The binding mechanism of HCN on the Fe(100), Fe(111) and Fe(110) surfaces is also analyzed by Mulliken charge population and the density of states in HCN. The result indicates that the configurations in which the adsorbed HCN becomes the non-linear are beneficial to the formation of the addition reaction for hydrogen. The nature that the introduction of Fe into the catalyst could increase the catalytic activity of the bimetallic catalyst in the addition reaction of hydrogen for nitriles is revealed.     

An ONIOM and DFT study of water adsorption on rutile TiO2 (110) cluster

Density functional theory (DFT) calculations performed at ONIOM DFT B3LYP/6‐31G**‐MD/UFF level are employed to study molecular and dissociative water adsorption on rutile TiO₂ (110) surface represented by partially relaxed Ti₂₅O₃₇ ONIOM cluster. DFT calculations indicate that dissociative water adsorption is not favorable because of high activation barrier (23.2 kcal/mol). The adsorption energy and vibration frequency of both molecularly and dissociatively adsorbed water molecule on rutile TiO₂ (110) surface compare well with the values reported in the literature. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Comparative DFT study of N2 and no adsorption on vanadium clusters Vn (n = 2–13)

Using gradient‐corrected density functional theory, we have comparatively studied the adsorption properties of diatomic molecules N₂ and NO on vanadium clusters up to 13 atoms. Spontaneous dissociation is found for N₂ adsorbing on V_n with n = 4–6, 12, and for NO with n = 3–12, respectively, whereas for the rest of the clusters, N₂ (NO) molecularly adsorbs on the cluster for all the possible sites. The incoming N₂ retains the magnetism of V_n except for V₂ and V₆ whose moments are quenched from 2 μ_B to zero. Consequently, the moments of V_nN₂ (n = 2–13) show even/odd oscillation between 0 and 1 μ_B. On the adsorption of NO, the magnetic moments of V_n with closed electronic shell are raised to 1 μ_B at n = 4, 8, and 10, and 3 μ_B at n = 12, whereas for open shell clusters, their magnetic moments increase for n = 5 and 9 and decrease for n = 2, 3, 5–7, 11, and 13 by 1 μ_B. These findings are rationalized by combinatory analysis from several aspects, for example, the geometry and stability of bare clusters, charge transfer induced by the adsorption, feature of frontier orbitals, and spin density distribution. © 2012 Wiley Periodicals, Inc.     

Si（NCO）^＋2结构与稳定性的密度泛函理论研究

使用密度泛函（DFT）方法对Si(NCO)^ 2的可能异构体进行了计算研究,在UB3LYP／6－311G（d)理论级别下得到了6种异构体的能量和振动频率,结果表明,以2个NCO基团直接与Si^ 配位形成的异体最为稳定,理论计算得到一个以2个CO分子对称方式吸附于SiN^2 两侧而形成的络合物,这个络合物是否存在需进一步证实,在UB3LYP／6－311g(D) Ez级别下,反应Si^ 2NOC→Si(NCO)^ 2的焓变为－751．94kJ/mol,说明此反应在能量上相当有利。     

CeO2(100)极性面结构与活性的密度泛函理论研究

CeO2是一类使用非常广泛的稀土氧化物催化材料,在许多重要的催化反应过程,如机动车尾气净化、水汽转换、石油裂解等,表现出很高的活性.大量研究表明,CeO2的高活性来源于其表面晶格氧,正是由于这些晶格氧能够直接参与氧化反应,同时反应留下的氧空位又能够被气相氧分子吸附填补,因而体现出很好的储放氧催化性能.目前多数研究采用CO氧化为模型反应,研究了CeO2常见的(111)和(110)晶面的晶格氧活性,但对于其另外一种重要低指数晶面(100)的结构和活性研究却非常有限.需要指出的是,CeO2(100)是一种极性表面,这给该表面的模型构建和理论研究带来了困难.为了深入了解这种极性表面的结构稳定性和催化活性,本文运用在位库仑力校正的密度泛函理论(DFT+U)方法系统研究了CeO2(100)极性面的可能结构及相关稳定性,并且深入分析了CO在该表面上的吸附和反应.本文首先利用板层模型尝试构建稳定的CeO2(100)极性面结构,方法是在保证整个板层化学计量配比完整的前提下,在表层或体相去除氧原子,同时使得整个板层上下对称不存在极性以利于计算.通过计算发现,在CeO2(100)表层分布氧空位的结构比体相中分布氧空位的结构要稳定,同时,氧空位的分布越接近表面,CeO2(100)面的结构稳定性就会越高,其最稳定的结构是将表层满覆盖氧离子移除一半.对CeO2(100)面不同结构的稳定性及相关电子结构分析表明,CeO2(100)表层满覆盖的氧离子间存在很强的相互排斥作用,因此倾向于降低表面氧浓度来提高表面的稳定性.另外,这种相互作用会降低相邻氧离子的价态,并能引起体相铈离子在整体表面维持完整的化学计量比的情况下,仍能出现局域4?电子而被还原为三价铈.随后我们研究了CO在CeO2(100)最稳定和次稳定表面上的氧化反应.发现CO在不同CeO2(100)表面的氧空位处吸附较强,另外,CO在CeO2(100)最稳定结构上可与表面晶格氧反应形成吸附的CO2中间物种,中间物种可直接解离成气相CO2,也可以继续与表面晶格氧反应形成碳酸盐.而在CeO2(100)次稳定表面上,CO很难与表面晶格氧形成吸附的CO2中间态,而直接产生气态CO2.     

噻吩在Ni(100),Cu(100),Co(100)表面吸附的密度泛函研究

采用密度泛函理论对噻吩分子在Ni(100),Cu(100)和Co(100)表面的吸附构型进行了GGA/PBE水平上的计算,通过比较吸附能及各结构参数,预测了各金属的脱硫活性.结果表明:噻吩在Ni表面发生了作用力较强的化学吸附,噻吩的S—C键有解离趋势;在Cu表面发生的是作用力较弱的物理吸附,噻吩分子构型并未发生较大变化;而噻吩在Co表面的吸附作用最强,噻吩的S—C键已经发生解离,和Co原子之间的距离已经达到甚至短于Co—S键的键长.这说明,金属的吸附脱硫活性为CoNiCu,与实验研究结果一致.此3种金属最稳定的分子吸附位均为hol45位.     

H_2O对SO_2在CaO表面上吸附的影响理论研究

采用密度泛函理论研究了H_2O对SO_2在CaO(001)表面上吸附的影响。结果表明,以四种形式(-H_2O、-H、-OH和-H-OH)存在的H_2O使SO_2在CaO表面上的吸附构型发生改变。SO_2在不同形式H_2O基团邻位吸附时,-H使S原子的p轨道态密度峰明显左移且吸附能比洁净表面大90 kJ/mol,其余基团表面吸附能无明显变化;SO_2吸附于-OH和-H-OH生成HSO_3基团,吸附能相比于洁净表面较小,可能作为暂态结构;SO_2吸附于-H_2O生成SO_3基团,H_2O断键生成的H基团起主要吸附作用,CaO表面上生成类似Ca(OH)_2的局部结构且吸附能比洁净表面大45 kJ/mol。     

Density functional theory for adsorption of HCHO on the FeO（100） surface

The density functional theory (DFT) and periodic slab model were used to get information concerning the adsorption of HCHO on the FeO(100) surface. A preferred η2-(C,O)-di-σ four-membered ring adsorption conformation on the Fe-top site was found to be the most favorable structure with the predicted adsorption energy of 210.7 kJ/mol. The analysis of density of states, Mulliken population, and vibrational frequencies before and after adsorption showed clear weakening of the carbonyl bond, and high sp3 charact...