A DFT Study of 2-Bromothiophene Adsorption on the Rh(111)Surface

Adsorption behaviors of 2-bromothiophene on the Rh（111） surface were discussed with DFT. The results revealed that adsorption at the parallel hol site and bridge site was the most stable. After adsorption, bond length of 2-bromothiophene changed significantly. Molecular plane was distorted, and C-H （Br, S） in the molecule was oblique and upswept against the metal surface. Vertical adsorption site was less stable than the plane adsorption site, but there was no distortion for the thiophene ring after adsorption. Aromaticity of 2-bromothiophene was destroyed at the hol and bridge adsorption sites, and the carbon atom in the thiophene ring presented quasi-sp3 hybfidizaton. After adsorption at the parallel hol, 2-bromothiophene obtained 0.86 electrons in total, and Rh（111） surface lost 2.08 electrons in all.

A DFT Study of Thiophene Adsorption on the Rh(111) Surfaces

Thiophene adsorption on the Rh（111） surfaces has been investigated by density functional theory.The results show that the adsorption at the hollow and bridge sites is the most stable.The molecular plane of the thiophene ring is distorted,the C=C bond is stretched to 1.448 and the C–C bond is shortened to 1.390.The C–H bonds tilt 22～42oaway from the surface.The calculated adsorption geometries are in reasonable agreement with population analysis and density of states.The thiophene molecule obtains 0.74 electrons, reflecting the interaction between the lone pair of sulfur and the d-orbitals of metal. The reaction paths and transition states for desulfurization of the molecule have been investigated. The bridge adsorption structure of thiophene leads to a thiol via an activated reaction with an energetic barrier of 0.30 eV. This second step is slightly difficult, and dissociation into a C4H4 fragment and a sulfur atom is possible, with an energetic barrier of 0.40 eV.

MnO_(x)/Rh(111)模型表面的制备及其CO加氢催化性能研究

金属-氧化物载体界面在多相催化中起着至关重要的作用.本研究制备了MnO_(x)/Rh(111)模型表面,采用原位镜面反射红外吸收光谱(IRAS)、扫描隧道显微镜(STM)、俄歇电子能谱(AES)和低能电子衍射(LEED)对其进行表征,并考察其在真空高温退火处理下的稳定性和CO加氢催化性能.结果显示:在Rh(111)单晶上沉积了规整有序且热稳定性好的不同覆盖度的MnO_(x)薄膜,MnO_(x)在Rh(111)上逐层生长,并在亚单层时形成清晰的二维团簇;低覆盖度时MnO_(x)二维簇以MnO的形式优先生长在Rh(111)的台阶位,并大多呈三角形,在亚单层Rh-MnO_(x)界面周边估测的长度随MnO_(x)覆盖度呈火山型变化,在0.4~0.5 ML(单层)之间有最大值.Rh(111)表面上CO加氢反应主要生成甲烷,部分覆盖MnO_(x)后显著抑制甲烷的生成而乙醇的选择性显著提高,且MnO_(x)盖满单层以后表面的催化活性下降.这些结果表明Rh-MnO_(x)界面位点可能是CO加氢生成乙醇的活性中心.

DFT Investigation of the Adsorption/dissociation Mechanisms of Methyl Nitrite on the Pd(111) Surface

The adsorption behavior of methyl nitrite （MN） on the closed-packed Pd（111） sur- face has been investigated in detail by using density functional theory （DFT）. MN binds to the surface in two alternative forms, using the nitrogen atom attached to the surface. An overall net charge transfer from the substrate to the cis-MN molecule is also confirmed. In addition, the reaction mechanism for the dissociation of MN on the Pd（111） surface has been identified and compared with the methanol decomposition via O-H scission. The results demonstrate that MN is a more active reactant than methanol for the oxidative addition to the Pd catalyst. The possible reason has been analyzed from the adsorption behaviors and reaction barriers, that is, MN is chemically absorbed on the Pd（111） surface; the CHaO-NO bond scission, leading to the formation of adsorbed methoxy species, is much more favorable than that of the O-H bond scission and has a large exothermic behavior.

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

Adsorption of CH3O at four sites （top, bridge, hcp, fcc） on Au（111） surface has been investigated by density functional theory method at the generalized gradient approximation level. We have performed calculations on adsorption energies, structures, Mulliken charges and vibrational frequencies of CH3O on Au（111） surface with full-geometry optimization. The predicted results are compared with the available experimental observation. The calculated CH3O adsorption structure and stretching vibrational frequencies agree well with experimental ones, and precise determinations of adsorption sites are carded out. The most favorite adsorption on Au（111） occurs at the bridge site, and O-C axis is tilted to the surface. However, on hollow sites （hcp, fcc） the species is adsorbed in an upright geometry （pseudo-C3v local symmetry）.

First-principles Study on Geometric and Electronic Structures of Si（111）-√7× √3-In Surface Reconstruction

In order to determine the structures of Si（111）-√7 √3-In surfaces and to understand their electronic properties, we construct six models of both hexagonal and rectangular types and perform first-principles calculations. Their scanning tunneling microscopic images and work functions are simulated and compared with experimental results. In this way, the hex-H3＇ and rect-T1 models are identified as the experimental configurations for the hexagonal and rectangular types, respectively. The structural evolution mechanism of the In/Si（lll） surface with indium coverage around 1.0 monolayer is discussed. The 4×1 and -√7× √3 phases are suggested to have two different types of evolution mechanisms, consistent with experimental results.

DFT Study of Thiophene Adsorption on the Pd(111) and Pt(111) Surfaces

Thiophene adsorption on the（111） surfaces of Pd and Pt have been investigated by density functional theory.The results indicate that the adsorption at the hollow sites is the most stable.To our interest,the molecular plane of thiophene ring is distorted with C=C bond being elongated to 1.450 and C–C bond being shortened to 1.347 ,and the C–H bonds tilt 13.91～44.05o away from this plane.Furthermore,analysis on population and density of states verified the calculated adsorption geometries.Finally,charge analysis suggests that thiophene molecule is an electron acceptor,reflecting the interaction between the lone pair of sulfur and the d-orbitals of metal.

Theoretical Study on the Adsorption and Decomposition of Methanol over the Pt-Mo(111)/C Surface

The density functional theory（DFT） and self-consistent periodic calculation were used to investigate the methanol adsorption on the Pt-Mo（111）/C surface.The adsorption energies,equilibrium geometries and vibration frequencies of CH3OH on nine types of sites on the Pt-Mo（111）/C surface were predicted and the favorite adsorption site for methanol is the top-Pt site.Both sites of valence and conduction bands of doped system have been broadened,which are favorable for electrons to transfer to the cavity.The possible decomposition pathway was investigated with transition state searching and the calculation results indicate that the O-H bond is first broken,and then the methanol decomposes into methoxy.The activation barrier of O-H bond breaking with Pt-Mo catalyst is only 104.8 kJ mol-1,showing that carbon supported Pt-Mo alloys have promoted the decomposition of methanol.Comparing with the adsorption energies of CH3OH on the Pt（111）/C surface and that of CO,the adsorption energies of CO are higher,and Pt（111）/C is liable to be oxidized and loses the activity,which suggests that the catalyst Pt-Mo（111）/C is in favor of decomposing methanol and has better anti-poisoning ability than Pt（111）/C.

Surface Regional Heat(Cool) Island Effect and Its Diurnal Differences in Arid and Semiarid Resource-based Urban Agglomerations

With the rapid development of urban agglomerations in northwest arid and semiarid regions of China, the scope of the urban heat island(UHI) effect has gradually expanded and gradually connected, and has formed a regional heat island(RHI) with a larger range of impact to the regional environment. However, there are few studies on the heat island effect of urban agglomerations in arid and semiarid regions, so this paper selects the urban agglomeration of Hohhot, Baotou and Ordos(HBO) of Inner Mongolia, China as the study area. Based on the 8-day composite Moderate-resolution Imaging Spectroradiometer(MODIS) surface temperature data(156scenes in all) and land use maps for 2005, 2010, and 2015, we analyze the spatiotemporal distributions of regional heat(cool) islands(RH(C)I) and the responses of surface temperatures to land-use changes in the diurnal and interannual surface cities. The results showed that: 1) from 2005 to 2015, urban areas showed the cold island effect during the day, with the area of the cold island showing a shrinking feature;at night, they showed the heat island effect, with the area of the heat island showing a first decrease and then an increase.2) From 2005 to 2015, the land development(unutilized land to building land) brings the greatest temperature increase(ΔT = 1.36°C)during the day, while the greatest temperature change at night corresponds to the conversion of cultivated land to building land(ΔT =0.78°C) exhibited the largest changes at night. From 2010 to 2015, the land development(grassland to building land) bring the greatest temperature increase(ΔT = 0.85°C) during the day, while the great temperature change at night corresponds to the conversion of water areas to building land(ΔT = 1.38°C) exhibited the largest changes at night. Exploring the spatial and temporal evolution of surface urban heat(cool) islands in urban agglomerations in arid and semiarid regions will help to understand the urbanization characteristics of urban agglomerations and provide a reference for the formulation of policies for the coordinated and healthy development of the region and co-governance of regional environmental problems.

Adsorption behavior of Fe atoms on a naphthalocyanine monolayer on Ag(111) surface

Adsorption behavior of Fe atoms on a metal-free naphthalocyanine（H2Nc） monolayer on Ag（111） surface at room temperature has been investigated using scanning tunneling microscopy combined with density functional theory（DFT）based calculations. We found that the Fe atoms were adsorbed on the centers of H2Nc molecules and formed Fe–H2Nc complexes at low coverage. DFT calculations show that Fe sited in the center of the molecule is the most stable configuration, in good agreement with the experimental observations. After an Fe–H2Nc complex monolayer was formed, the extra Fe atoms self-assembled to Fe clusters of uniform size and adsorbed dispersively at the interstitial positions of Fe–H2Nc complex monolayer. Therefore, the H2Nc monolayer grown on Ag（111） could be a good template to grow dispersed magnetic metal atoms and clusters at room temperature for further investigation of their magnetism-related properties.

A Density Functional Theory Study on the Adsorption of CN on Ni(111) Surface

The interaction of cyanide (CN) with different sites on Ni(111) surface is studied by using density functional theory (DFT). Ni19 cluster is used to simulate the surface. The present calculations show that the end-on bonded (through C atom) configuration is much more preferable than the side-on bonded CN or other configurations on the same adsorption site. For all adsorption modes, adsorption energies at the top, bridge, and three-fold sites on Ni(111) are comparable, with the bridge site of the end-on bonded CN (through C atom) more favorable than other adsorption sites. CN vibrational frequencies are red-shifted at all cases, except that the end-on CN bonded (through C atom) on the top site is blue-shifted. The bonding of CN on the Ni(111) surface is large- ly ionic.

Formation and local electronic structure of Ge clusters on Si（111）-7×7 surfaces

We report the formation and local electronic structure of Ge clusters on the Si（111）-7×7 surface studied by using variable temperature scanning tunnelling microscopy （VT-STM） and low-temperature scanning tunnelling spectroscopy （STS）. Atom-resolved STM images reveal that the Ce atoms are prone to forming clusters with 1.0 nm in diameter for coverage up to 0.12 ML. Such Ce clusters preferentially nucleate at the centre of the faulted-half unit cells, leading to the ＇dark sites＇ of Si centre adatoms from the surrounding three unfaulted-half unit cells in filled-state images. Biasdependent STM images show the charge transfer from the neighbouring Si adatoms to Ce clusters. Low-temperature STS of the Ce clusters reveals that there is a band gap on the Ce cluster and the large voltage threshold is about 0.9 V.

Acetonitrile(CH_3CN)and methyl isocyanide(CH_3NC) adsorption on Pt(111)surface:a DFT study

The adsorption of CH3CN and CH3NC on the Pt（lll） surface at the 1/4 monolayer （ML） coverage has been car-ried out at the level of density functional theory for understanding hydrogenation processes of nitriles. The most favored ad-sorption structure for CH3 CN is the C--N bond almost parallel to the surface with the C-N bond interaction with adjacent surface Pt atoms. For CH3NC, the most stable configuration is the CH3 NC locates at the face center cubic （fcc） site with the C-atom bonded to three Pt atoms. In addition, the HCN and HNC adsorption has been computed, and the adsorption pattern is nearly similar to the CH3CN and CH3NC, respectively. The adsorbed molecules rehybridize on the surface, be-coming non-linear with a bent C-C-N or C-N-C angle. Furthermore, the binding mechanism of these molecules on the Pt（111） surface is also analyzed.

The STM Images of Pt (111) (<img src="http://latex.codecogs.com/gif.latex?\sqrt{3}\times&space;\sqrt{3}"title="\sqrt{3}\times \sqrt{3}"/>)R30&deg;/CO Surface by DFT Calculations

In this work we have performed total-energy calculations of the chemisorption properties and STM images of Pt (111) ( × )R30°/CO Surface;STM Image;ChemisorptionR30°/CO surface by using the density functional theory (DFT) and the projector-augmented wave (PAW) method. The calculations show that carbon monoxide molecule (CO) adsorbs on FCC site in the Pt (111) ( × )R30°/ surface is energetically favored by the GGA-PBE XC-functional, this is in agreement with most of the theoretical calculations which is using different XC-functional at the most. However, these results strongly conflicted with the existing experiments. Actually the calculated work function for the FCC adsorption is quite different from the experiments while the atop one is in good agreement with experiments. We speculate that the atop adsorption for (CO is favorable for the adsorption case at the most. Furthermore, we have calculated the scanning tunneling microscopy (STM) images for both adsorption geometries and suggest that there should be existed remarkable differences in the STM images. The present work provides a faithful criterion accounting for the local surface geometry in Pt (111) ( × )R30°/CO surface from surface work functions and STM images instead of totalenergy calculations.

Adsorption of HCN on Ni/Pt(111)Bimetallic Surfaces Investigated with Density Functional Theory Method

We applied periodic density-functional theory to investigate the adsorption of HCN on x Ni@Pt（111） bimetallic surfaces（x = 1~4）. The results have been compared with those obtained on pure Ni（111） and Pt（111） surfaces. For all bimetallic surfaces,HCN is preferentially tilted with the CN bond parallel to the surface,and adsorption energies increase with an increasing number of layer Ni atoms on the surface. The adsorption energies of HCN on all bimetallic surfaces are larger than that on the Pt（111） surface,whereas the adsorption energies of HCN on 3Ni@Pt（111） and 4Ni@Pt（111） are larger than that on the Ni（111） surface,indicating that the introduction of Ni to the Pt catalyst could increase the activity of bimetallic catalyst in the hydrogenation reaction for nitriles. Larger adsorption energy of HCN leads to a longer C–N bond length and a smaller CN vibrational frequency. The analysis of Bader charge and vibrational frequencies showed obvious weakening of the adsorbed C–N bond and an indication of sp2 hybridization of both carbon and nitrogen atoms.

NO在Rh(100),Rh(111)面上吸附与直接分解的密度泛函理论研究

The chemisorption and direct decomposition of NO on Rh（100） and Rh（111） surfaces were studied by the density functional theory（DFT） with Dmol3 program.The calculation results show that for the Rh（100）surface,the bridge sites are found to be the preferred adsorption site,but for the Rh（111） surface,the three fold hollow（hcp） sites are found to be the most stable one;the transition states were confirmed for the direct decomposition of NO on Rh（100） and Rh（111） surfaces by successful transition state search,and the activation energy are 161.91 kJ/mol for Rh（100） and 183.72 kJ/mol for Rh（111）,respectively.

在Rh(111)面上NO＋CO反应机理的密度泛函理论研究

应用基于密度泛函理论赝势平面波方法的CASTEP程序,对Rh(111)上的NO+CO反应机理进行研究.对于反应中的各个关键步骤:NO离解、CO2生成、通过N2O离解生成N2以及通过N+N反应生成N2都进行了详细讨论,计算得到各反应步骤的过渡态以及活化能,从而确立了各步骤的反应路径.

CO在Pd掺杂Rh(111)表面吸附的理论研究

采用密度泛函理论与周期性平板模型相结合的方法,对CO在Rh(111)表面top、fcc、hcp、bridge四个吸附位和Rh-Pd(111)表面Rh-top、Pd-top、Rh Rh-bridge、Rh Pd-bridge、Pd Pd-bridge、Rh2Pdhcp、Rh Pd2-hcp、Rh2Pd-fcc、Rh Pd2-fcc九个吸附位的13种吸附模型进行了构型优化、能量计算,得到了CO较有利的吸附位;并对最佳吸附位进行总态密度分析.结果表明:CO在Rh(111)和Rh-Pd(111)表面的最稳定吸附位分别为Rh-hcp和Rh-top位,其吸附能的大小顺序为Ph(111)>Rh-Pt(111);CO与金属表面成键,属于化学吸附.

苯分子与Rh(111)面相互作用的分子轨道研究

用群分解EHMO法研究了苯在Rh(111)面上的化学吸附和成键性质。以Rh7原子簇模型模拟Rh(111)表面,得到结合能为41kJ/mol,吸附高度2.60。被吸附的苯分子通过π键和金属原子的d轨道相互作用而受到活化,有利于在(111)表而上的化学反应。

NO在Pt掺杂Rh(111)表面吸附的理论研究

采用密度泛函理论与周期性平板模型相结合的方法,对NO在Rh(111)表面top、fcc、hcp、bridge4个吸附位和Rh-Pt(111)表面Rh-top、Pt-top、RhRh-bridge、Rh Pt-bridge、Pt Pt-bridge、Rh2Pt-hcp、Rh Pt2-hcp、Rh2Pt-fcc、Rh Pt2-fcc 9个吸附位的13种吸附模型进行了构型优化、能量计算,得到了NO较有利的吸附位;并对最佳吸附位进行总态密度分析.结果表明:NO在Rh(111)和Rh-Pt(111)表面的最稳定吸附位分别为Rh-top和Pt-top位,其吸附能的大小顺序为Ph(111)<Rh-Pt(111);NO与金属表面成键,属于化学吸附.