Evaluation for the configurational and electronic state of SO3 adsorbed on Pt surface

We evaluate the adsorption of SO₃ molecule on the Pt (1 1 1) surface using the first-principles calculations by a slab model with a periodic boundary condition. We find that there are four stable adsorption configurations on the Pt surface, where SO₃ molecules are adsorbed above the three-fold fcc and hcp sites. In two of these configurations, S and two O atoms are bound to the Pt atoms, and in two other of them, all the three O atoms are bound to Pt surface atoms. Besides, it is found that molecular orbitals of SO₃ and those of Pt surface are hybridized in the active metal d-bands region, that the localized molecular orbitals in SO₃ are stabilized, and that the charge is transferred from Pt to S 3p by SO₃ adsorption on Pt surface though the other interaction of S and O (bound to Pt) component with Pt is little. In addition, the bond between S and O bound to Pt become weak by SO₃ adsorption on Pt surface because the charge polarization to O-Pt bond weakens the bond between S and O bound to Pt. This interaction is assumed to encourage the breakage of S-O bond.     

The local structure of SO2 and SO3 on Ni(1 1 1): A scanned-energy mode photoelectron diffraction study

O 1s and S 2p scanned-energy mode photoelectron diffraction (PhD) data, combined with multiple-scattering simulations, have been used to determine the local adsorption geometry of the SO₂ and SO₃ species on a Ni(1 1 1) surface. For SO₂, the application of reasonable constraints on the molecular conformation used in the simulations leads to the conclusion that the molecule is centred over hollow sites on the surface, with the molecular plane essentially parallel to the surface, and with both S and O atoms offset from atop sites by almost the same distance of 0.65 Å. For SO₃, the results are consistent with earlier work which concluded that surface bonding is through the O atoms, with the S atom higher above the surface and the molecular symmetry axis almost perpendicular to the surface. Based on the O 1s PhD data alone, three local adsorption geometries are comparably acceptable, but only one of these is consistent with the results of an earlier normal-incidence X-ray standing wave (NIXSW) study. This optimised structural model differs somewhat from that originally proposed in the NIXSW investigation.     

Theoretical study on adsorption of thiophenethiolate molecule on Au(1 1 1) surface

We have theoretically studied the adsorption of a thiophenethiolate (C₄H₃S-S) molecule on the Au(1 1 1) surface by first-principles calculations. It is found that the bridge site is the most stable adsorption site with the adsorption energy of 1.02 eV. In the optimized adsorption geometry, the bond between the head S atom and the connected C atom in the tail thiophene molecule is tilted by 57.2° from the surface normal. In addition, the adsorption of thiophenethiolate induces large relaxations of the surface Au atoms around it. Furthermore, weak interactions between the S atom in the tail thiophene ring and the Au atoms also contribute to the adsorption on the Au surface.     

The local structure of SO2 and SO3 on Ni(1 1 1)

The normal incidence X-ray standing wave (NIXSW) technique, supported by X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS), has been used to determine the local adsorption geometry of SO₂ and SO₃ on Ni(1 1 1). Chemical-state specific NIXSW data for coadsorbed SO₃ and S, formed by the disproportionation of adsorbed SO₂ after heating from 140 K to 270 K, were obtained using S 1s photoemission detection. For adsorbed SO₂ at 140 K the new results confirm those of an earlier study [Jackson et al., Surf. Sci. 389 (1997) 223] that the molecule is located above hollow sites with its molecular plane parallel to the surface and the S and O atoms in off-atop sites; corrections to account for the non-dipole effects in the interpretation of the NIXSW monitored by S 1s and O 1s photoemission, not included in the earlier work, remove the need for any significant adsorption-induced distortion of the SO₂ in this structure. SO₃, not previously investigated, is found to occupy an off-bridge site with the C_3v axis slightly tilted relative to the surface normal and with one O atom in an off-atop site and the other two O atoms roughly between bridge and hollow sites. The O atoms are approximately 0.87 Å closer to the surface than the S atom. This general bonding orientation for SO₃ is similar to that found on Cu(1 1 1) and Cu(1 0 0) both experimentally and theoretically, although the detailed adsorption sites differ.     

多重散射团簇方法对吸附系统SO2/Ag(110)的理论分析

利用多重散射团簇方法(MSC)对吸附系统SO₂/Ag(110)的S原子K边X射线吸收精细结构谱(NEXAFS)作了理论分析.研究表明,覆盖度为0.5时,吸附的SO₂的S—O键长比气体状态时增长了(0.014±0.006)nm,OSO键角减小了15°±5°;SO₂分子的S原子处于芯位,但两个O原子处于不对称的位置;分子平面与(110)的夹角约为52°,同时分子平面相对衬底表面法线有一小角度的倾斜.MSC计算证实了该吸附系统存在一介于π^{关键词： X射线吸收精细结构 2/Ag(110)')" href="#">吸附系统SO₂/Ag(110) 多重散射团簇方法}     

First-principles calculations of hydrogen molecule adsorption on Ti (0 0 0 1)-(2 × 1) surface

Adsorption of H₂ molecule on the Ti (0 0 0 1)-(2 × 1) surface was studied by density functional theory with generalized gradient approximation (GGA). The parallel and vertical absorption cases were investigated in detail by adsorption energy and electronic structure analysis, we obtained three stable configurations of FCC-FCC (the two H atoms adsorption on the two adjacent fcc sites of Ti (0 0 0 1) surface, respectively), HCP-HCP (the two H atoms adsorption on the two adjacent hcp sites of Ti (0 0 0 1) surface, respectively) and FCC-HCP (the one H atom adsorption on the fcc site and the other adsorption on the near hcp site) based on the six different parallel adsorption sites after the H₂ molecule dissociates. However, all the end configurations of four vertical adsorption sites were unstable, H₂ molecule was very easy to desorb from Ti surface. The H-H bond breaking and Ti-H bond forming result from the H₂ molecule dissociation. H-H bond breaking length ranges from 1.9 Å to 2.3 Å for different adsorption configurations due to the strong Ti-H bond forming. The H₂ dissociative approach and the end stable configurations formation in parallel adsorption processes are attributed to the quantum mechanics steering effects.     

Adsorption of water molecule on (001) and (110) surfaces of MgH2

First principle calculations have been performed to explore the adsorption characteristics of water molecule on (001) and (110) surfaces of magnesium hydride. The stable adsorption configurations of water molecule on the surfaces of MgH₂ were identified by comparing the total energies of different adsorption states. The (110) surface shows a higher reactivity with H₂O molecule owing to the larger adsorption energy than the (001) surface, and the adsorption mechanisms of water molecule on the two surfaces were clarified from electronic structures. For both (001) and (110) surface adsorptions, the O p orbitals overlapped with the Mg s and p orbitals leading to interactions between O and Mg atoms and weakening the O–H bonds in water molecule. Due to the difference of the bonding strength between O and Mg atoms in the (001) and (110) surfaces, the adsorption energies and configurations of water molecule on the two surfaces are significantly different.     

Adsorption site preference of CO2 on the Pt(1 0 0) surface by ab initio calculations

This paper investigates the adsorption sites and electronic structure of the adsorption of CO₂ on the Pt(1 0 0) surface by ab initio periodic density functional theory (DFT) methods. Several parallel and vertical adsorption sites are examined in detail. The results show that the adsorption energy for the atop hollow horizontal (thh) site is 0.34 eV. However, other sites only have small binding energies and these values are very close. For an atop hollow horizontal site, the calculated elecronic interaction is contributed to not only the Pt-O atoms, but also Pt-C atoms. So the results indicate that the thh site is the most favorable and stable.     

The bonding geometry of alkylsilanes on gold: Relation to surface pattern development and STM image contrast

The adsorption of methylsilane (MeSiH₃) on Au(1 1 1) was investigated using density functional theory (DFT) within a generalized gradient approximation (GGA). Two preferred chemisorption sites are identified: the hollow site and an atop site with an ejected gold substrate atom. Both of these configurations result in a tetracoordinate Si with a distorted tetrahedral geometry. The energy of adsorption is calculated allowing an analysis of the preferred binding geometry as a function of coverage. The relation of the supermolecular length scale pattern that emerges from a spinodal decomposition of the two phases arising from the two binding geometries is discussed. The pattern observed in the STM images is shown to be consistent with the local density of states calculated for the two different binding geometries.     

The structure and bonding of furan on Pd(111)

The structure and bonding of molecular furan, C₄H₄O, on Pd(111) has been investigated using density functional theory (DFT) calculations and the results compared with those of a recent experimental investigation using scanned-energy mode photoelectron diffraction (PhD). The DFT results confirm the orientation of the molecular plane to be essentially parallel to the surface and show a clear energetic preference for one of the two possible structures identified in the PhD study, namely that with the molecule centred over the hollow sites of the surface. Two slightly different geometries at the hollow sites are found to be essentially energetically equivalent; in both cases, one Pd surface atom bonds to two C atoms, while two other Pd atoms each bond to one C atom. These structures differ in that in one case the pair of C atoms bonding to a single Pd atom are both β-C (C atoms not bonded to O in the furan molecule), whereas in the second case this pair of C atoms comprises one β-C and one α-C (adjacent to the O atom in furan). In both structures the C–Pd bonding is accompanied by displacements of the H and O atoms away from the surface and out of the molecular plane and local C–Pd coordination consistent with a rehybridisation of the C bonding to sp³ character.     

乙烯和乙炔基在Ni(110)表面上吸附结构的研究

采用平面波赝势方法，利用基于从头计算的软件包，对乙烯和乙炔基在Ni(110)表面上吸附的问题进行了计算. 在低覆盖度时，孤立的乙烯分子的吸附能比密集时高，乙烯分子的C-C 轴大致沿衬底的Ni原子链方向(即沿［110］晶向)，C-C轴与衬底Ni(110)表面有12°的倾斜角，乙烯分子的C—C键的键长为 0.147nm. 乙烯分子中接近顶位的C原子与衬底中距离最近的Ni原子为0.199nm. 在高覆盖度时，乙烯分子在Ni(110)表面上形成c(2×4)再构，每个表面二维元胞中有两个乙烯分子，每个乙烯分子的吸附位置与低覆盖度时相似，而C—C键长比低覆盖度时要短. 乙炔基是乙烯在Ni(110)表面上分解的产物. 关于乙炔基的计算结果表明：乙炔基的两个C原子的间距为0.131nm，比乙烯分子中C原子的间距更短. 与乙烯分子相比，乙炔基的吸附位置更靠近顶位. H原子与吸附在顶位上的C原子相连接，C—H键也大致沿衬底的Ni原子链方向，与Ni表面呈45°的倾斜角. 关键词： 乙烯和乙炔基 平面波赝势方法 吸附几何结构     

(TiO2)n(n=3—6)团簇吸附水分子的理论研究

给出了优化小分子在团簇表面吸附结构的遗传算法.结合经验势函数,搜寻了水分子在(TiO₂)_n(n=3—6)团簇上可能的吸附方式;利用B3LYP/6-31G^**方法对各种吸附结构进行了优化.结果表明水分子主要通过O原子以非解离方式吸附到团簇中配位数较低或位置比较凸出的Ti原子上.分子轨道分析表明,水分子与团簇之间的成键主要来自吸附位Ti原子3s3p轨道的贡献,水分子的轨道保持了气相水分子中的基本特征,但离域化程度增大 关键词： 2团簇')" href="#">TiO₂团簇 2O吸附')" href="#">H₂O吸附 遗传算法 DFT     

Adsorption and dissociation of ammonia on Au(1 1 1) surface: A density functional theory study

Periodic density functional theory (DFT) calculations using plane waves had been performed to systematically investigate the stable adsorption amine and its dehydrogenated reaction on Au(1 1 1) surface. The equilibrium configuration including on top, bridge, and hollow (fcc and hcp) sites had been determined by relaxation of the system. The adsorption both NH₃ on top site and NH₂ on bridge site is favorable on Au(1 1 1) surface, while the adsorption of NH on hollow (fcc) site is preferred. The adsorbates are adsorbed on the gold surface with the interaction between p orbital of adsorbate and the d orbital of gold atoms. The interaction between adsorbate and gold slab is more evident on the first layer than on any others. Furthermore, the dissociation reaction of NH₃ on clean gold surface, as well as on the pre-covered oxygen atom and pre-covered hydroxyl group surface had been investigated. The results show that the dehydrogenated reaction energy barrier on the pre-covered oxygen gold surface is lower. The adsorbed O can promote the dehydrogenation of amine. Additionally, OH as the product of the NH₃ dissociation reaction participates in continuous dehydrogenation reaction, and the reaction energy barrier is the lowest (22.77 kJ/mol). The results indicated that OH_ads play a key role in the dehydrogenated reaction on Au(1 1 1) surface.     

Water adsorption on the Be(0001) surface: from monomer to trimer adsorption

In this paper, the density functional theory has been used to perform a comparative theoretical study of water monomer, dimer, trimer, and bilayer adsorptions on the Be(0001) surface. In our calculations, the adsorbed water molecules are energetically favoured adsorbed on the atop sites, and the dimer adsorption is found to be the most stable with a peak adsorption energy of ～437 meV. Further analyses have revealed that the essential bonding interaction between the water monomer and the metal substrate is the hybridization of the water 3a₁-like molecular orbital with the (s, p_z) orbitals of the surface beryllium atoms. While in the case of the water dimer adsorption, the 1b₁-like orbital of the H₂O molecule plays a dominant role.     

MoSi_2(001)表面的氧吸附行为

运用第一原理密度泛函理论方法,首先计算了MoSi_2各清洁表面的表面能,(001)Si-|-Si断面具有较低的表面能,是MoSi_2最可能的解理面;通过生成能及键布居分析研究了单氧原子、双氧原子及氧分子在(001)Si-|-Si断面的吸附行为,发现单氧原子在空位处吸附最稳定,此时O极易与Si结合,得到的Si-O-Si键长及键角与SiO_2的非常接近,表明低浓度下O极易与表面的Si结合生成SiO_2;双氧原子发生空位+顶位吸附时O原子除与Si有强作用外,可与Mo有一定相互作用;氧分子以平行的方式接近空位最有利于吸附,此时氧分子最易分解为氧原子,发生氧原子在空位的吸附.     

A theoretical investigation on Pt3Sn(1 0 2) surface alloy and CO-Pt3Sn(1 0 2) system

The adsorption properties of CO on experimentally verified stepped Pt₃Sn(1 0 2) surface were investigated using quantum mechanical calculations. The two possible terminations of Pt₃Sn(1 0 2) were generated and on these terminations all types of possible adsorption sites were determined. The adsorption energies and geometries of the CO molecule for all those sites were calculated. The most favorable sites for adsorption were determined as the short bridge site on the terrace of pure-Pt row of the mixed-atom-ending termination, atop site at the step-edge of the pure row of pure-Pt-ending termination and atop site at the step-edge of the pure-Pt row of the mixed-atom-ending termination. The results were compared with those for similar sites on the flat Pt₃Sn(1 1 0) surface considering the fact that Pt₃Sn(1 0 2) has terraces with (1 1 0) orientation. The LDOS analysis of bare sites clearly shows that there are significant differences between the electronic properties of Pt atoms at stepped Pt₃Sn(1 0 2) surface and the electronic properties of Pt atoms at flat (1 1 0) surface, which leads to changes in the CO bonding energies of these Pt atoms. Adsorption on Pt₃Sn(1 0 2) surface is in general stronger compared to that on Pt₃Sn(1 1 0) surface. The difference in adsorption strength of similar sites on these two surface terminations is a result of stepped structure of Pt₃Sn(1 0 2). The local density of states (LDOS) of the adsorbent Pt and C of adsorbed CO was utilized. The LDOS of the surface metal atoms with CO-adsorbed atop and of their bare state were compared to see the effect of CO chemisorption on the electron density distribution of the corresponding Pt atom. The downward shift in energy peak in the LDOS curves as well as changes in the electron densities of the corresponding energy levels indicate the orbital mixing between CO molecular orbitals and metal d-states. The present study showed that the adsorption strength of the sites has a direct relation with their LDOS profiles.     

Effects of N adsorption on the structural and electronic properties of SrTiO3(0 0 1) surface

The atomic configurations, bonding characteristics, and electronic structures of the N-adsorbed (directly and substitutionally) SrTiO₃(0 0 1) surface are studied by using first-principles method based on the density functional theory. From the analysis of the energetics and density of states, it is found that the stability of the directly adsorbed N depends on the relative position of N atom to the surface. To better understand the effects of the substitutionally adsorbed N on the surface, as an example, the behavior of Au atoms adsorbed on the N-substituted surface is discussed in detail. There is clearly a synergy effect between the substitution of N for O_s(I) and the adsorption of Au atoms on the SrTiO₃(0 0 1) surface.     

Comprehensive evolution mechanism of SOx formation during pyrite oxidation

Pyrite (FeS₂) oxidation during coal combustion is one of the main sources of harmful SO₂ emission from coal-fired power plants. Density functional theory (DFT) study was performed to uncover the evolution mechanism of SO_x formation during pyrite oxidation. The results show that chemisorption mechanism is responsible for O₂, SO₂ and SO₃ adsorption on FeS₂ surface. The presence of formed oxidation layer (Fe₂O₃) weakens the interaction between O₂ molecule and FeS₂ surface. The adsorbed O₂ molecule easily dissociates into active surface O atom for SO_x formation. The dissociation reaction of O₂ is activated by 77.38?kJ/mol, and exothermic by 138.46?kJ/mol. Compared to the further oxidation of SO₂ into SO₃, SO₂ prefers to desorb from FeS₂ surface. The dominant reaction pathway of SO₂ formation from the oxidation of the outermost FeS₂ surface layer is a three-step process: surface lattice S oxidation, SO₂ desorption and replenishment of S vacancy by activated surface O atom. The elementary reaction of surface lattice S oxidation has an activation energy barrier of 197.96?kJ/mol, and is identified as the rate-limiting step. SO₂ formation from the further oxidation of bulk FeS₂ layer is controlled by a four-step process: bulk lattice S migration, lattice S oxidation, SO₂ desorption and surface O atom deposition. Migration of lattice S from bulk position to the outermost surface shows a high activation energy barrier of 175.83?kJ/mol. The deposition process of surface O atom is a relatively easy step, and is activated by 21.05?kJ/mol.     

Ab-initio pseudopotential study of electronic structure and chemisorption of oxygen on aluminium surface

Chemisorption of oxygen atom on aluminium (1 1 1), (1 1 0) and (1 0 0) surfaces is studied using ab-initio plane wave pseudopotential method based on density functional theory (DFT). Oxygen atom chemisorbed on three different high symmetry sites; top, short-bridge and hollow sites on the aluminium surfaces are examined. It has been found that the O-adatom adsorbed at the hollow site on aluminium (1 1 1), (1 1 0) and (1 0 0) plane yield energetically most stable structure. Calculation of chemisorption energies of O-adatom on aluminium surfaces shows that oxygen is most strongly bound to aluminium atoms on Al(1 1 1) plane and the calculated value of the chemisorption energy of O-adatom at the hollow site on Al(1 1 1) surface is 4.8 eV. In this work, the chemisorption energies calculated for O-adatom on Al(1 1 0) and Al(1 0 0) surfaces are reported for the first time. The electronic structures and the electronic charge density distributions of the oxygen chemisorbed aluminium surfaces are also investigated. Calculations show that for aluminium, p orbitals also contribute significantly along with the s orbitals during the bond formation with oxygen atom. Therefore, the possibilities of hybridizations lead to the strong bonding configurations.     

Adsorption of SH and OH and coadsorption of S, O and H on Ni(111)

The adsorption of SH and OH radicals on Ni(111) is treated using an ab initio embedding theory. The Ni(111) surface is modeled as a three-layer, 28-atom cluster with the Ni atoms fixed at bulk lattice sites. The Ni(111) energy surface is very flat for SH adsorption if the H tilt angle is allowed to vary. At both atop and bridge sites, the S---H axis is tilted away from the surface normal by 70°, resulting in the sulfur atom being sp³-hybridized and the adsorption energy being 59 kcal mol⁻¹. For SH at the three-fold site, the S---H axis is normal to the surface, the sulfur is sp-hybridized, and the adsorption energy is 58 kcal mol⁻¹. OH is preferentially adsorbed at the three-fold site. The calculated adsorption energy is 90 kcal mol⁻¹ and the O---H axis is perpendicular to the surface. OH adsorption at the atop and bridge sites is 16 and 5 kcal mol⁻¹ less stable than at the three-fold site, respectively. Atomic H, O and S are preferentially adsorbed at the three-fold site. The calculated adsorption energies are 62, 92 and 87 kcal mol⁻¹, for H, O and S, respectively. The calculated adsorbate---Ni bond distances of 1.86 Å for H, 1.86 Å for O and 2.29 Å for S are in good agreement with experimental data. SH and OH bonding to the surface involves a combination of ionic and covalent contributions and substantial mixing with the Ni 3d orbitals. Dipole-moment calculations indicate strong ionic bonding for the atomic O/Ni system and ionic plus covalent character for the atomic S/Ni interactions. Adsorption of S and O at the three-fold site blocks H adsorption at the nearby surface. Moving H away from the S or O adatom reduces the repulsion. The dissociation of SH_ad → S_ad + H_ad is calculated to be exothermic by 5 kcal mol⁻¹ and OH_ad → O_ad + H_ad to be endothermic by 30 kcal mol⁻¹ for infinite separation between S, O and H.