Li和Al掺杂的MgO(001)表面负载W_3O_9团簇的构型与电子结构

采用基于第一性原理的分子动力学和量子力学相结合的方法,对W3O9团簇在经Li和Al原子掺杂的MgO(001)表面的负载构型、稳定性以及体系的电子结构进行了系统研究.结果表明,当掺杂发生在表层时,杂质原子的类型对W3O9团簇的负载构型有显著影响.对于缺电子的Li掺杂,负载后W3O9团簇环状构型并不稳定,转化为链状结构;而Al原子的掺杂则使得MgO(001)表面电子富余,此时W3O9团簇存在平躺和垂直两种吸附方式,二者能量稳定性相近,其中前者存在同时与三个W原子成键的帽氧结构.当掺杂发生在次表层时,两种掺杂体系W3O9的负载构型相似,团簇仍保持环状结构并倾向于采用垂直方式沉积在表面上.与Li掺杂体系相比,富电子的Al掺杂可显著增强W3O9与MgO(001)表面之间的结合能力,负载后有较多电子从表面转移到团簇中特定的W原子上,这将对W3O9团簇的催化性能产生显著影响.     

Pt原子在γ-Al2O3(001)表面的吸附及迁移

采用密度泛函理论(DFT)中广义梯度近似(GGA)方法, 对Pt原子与γ-Al₂O₃(001)面的相互作用及迁移性能进行了研究. 分析了各种可能吸附位及吸附构型的松弛和变形现象, 吸附能和迁移能垒的计算结果表明: Pt团簇能够稳定吸附在该表面. Pt原子在表面O位的吸附能明显较高, 这主要是由Pt向基底O原子转移了电子所致. 电荷布居分析表明, Pt原子显电正性, Pt和Al原子之间存在排斥作用, 导致与Al原子产生较弱相互作用. 计算的平均吸附能大小依赖于Pt团簇的大小和形状, 总体趋势是随着Pt原子数增多, 吸附能降低. Pt原子在γ-Al₂O₃(001)表面迁移过程所需克服的迁移能垒最高值为0.51 eV. 随着吸附的Pt原子数增多,更倾向于形成Pt团簇. 因此, Pt原子在γ-Al₂O₃(001)表面的吸附演变不可能形成光滑、均匀平铺的吸附构型, 而在一定条件下容易出现团聚.     

硼碳团簇BnC2 (n＝1～6)的理论研究

应用密度泛函理论在B3LYP/6-311＋G(d)水平上研究了硼碳团簇B_nC₂ (n＝1～6)的几何结构、生长机制和相对稳定性. 计算结果表明, 对于n＝2～6的簇, 平面多环状构型为最稳定的结构, 其中C原子分布于环的顶点、有尽可能多的三配位硼原子和尽可能多的B—C键. 碳原子作为杂原子倾向掺杂于团簇的顶点位置, 它的掺杂不改变硼团簇的主体结构. 与平面多环状结构相比, 随着簇尺寸的增大, 三维结构和线性链结构更不稳定. 在低能线性结构中, C原子位于链两侧的第二个位置. 计算的碎片分裂能、递增键能以及HOMO-LUMO能隙表明, B₄C₂为幻数簇.     

AlmN2和AlmN2＋ (m＝1～8)团簇结构与稳定性的量子化学研究

用密度泛函理论(DFT)的B3LYP方法, 在6-311G*水平上对Al_mN₂和Al_mN₂^＋ (m＝1～8)团簇的几何构型、电子结构、振动频率和分子轨道进行了理论研究. 结果表明, Al_mN₂类团簇的基态结构有两种基本构型, 一种是以N—N键为核心周围与Al原子相配位形成的, 一种是由两个Al_nN (n≤m/2)分子碎片通过共用Al原子或Al—Al键相互结合形成的. 对Al_nN分子碎片相互结合形成结构的绝热电离能讨论得到, m为偶数的团簇比m为奇数的稳定.     

过渡元素掺杂Fe3O4（001）表面磁电性能的理论研究

采用基于密度泛函理论的第一性原理方法,计算Fe₃O₄,Fe₃O₄（001）表面以及过渡元素掺杂表面的电子结构和磁性。结果表明Fe₃O₄的半金属性主要来源于B位Fe离子,并且Fe的3d轨道发生强烈自旋极化;比较（001）表面不同终端A和B终端的表面能和电子结构,得出两种终端稳定性存在差异且A终端较稳定同时表现半金属性;由过渡元素V、Cr、Mn、Co、Cu和Zn取代Fe₃O₄（001）表面A终端A位Fe进行掺杂,形成的6种新表面结构都保持了半金属性。对比它们的表面能和磁矩,Mn掺杂的表面结构最稳定并且磁矩明显增大。     

TinO2和TinO2-(n=1-10)团簇的几何结构、电子和磁性质

基于密度泛函理论(DFT)的B3LYP方法, 研究了Ti_nO₂和Ti_nO₂^- (n=1-10)团簇的几何结构、电子结构以及磁性. 结果表明, 两个氧以分离的原子状态吸附在金属团簇的表面, 呈现出以一个钛原子为中心的O-Ti-O 的相邻吸附形式. 中性团簇和阴离子团簇的能量最低结构相似. 稳定性分析表明Ti_nO₂具有很高的稳定性, 特别是TiO₂和Ti₇O₂. 此外, 详细讨论了团簇的电离势、电子亲和能、电子解离能和能隙. 基于最低能量结构, 讨论了团簇的磁性, 发现电荷从Ti 原子向O原子转移, 并且电荷转移主要发生在Ti_nO₂的Ti-3d、Ti-4s和O-2p轨道. 磁性团簇中反铁磁序占据主导, 磁矩主要来源Ti-3d电子的贡献, 而两个氧原子的贡献非常小.     

基于密度泛函理论分析团簇ConMoS(n=1~5)电子性质、光学性质及磁性

为了从理论层面深入探究团簇Co_nMoS （n=1~5）的电子性质、光学性质及磁性,弄清其内在关联,依据拓扑学原理和密度泛函理论,在B3LYP/def2-TZVP量子化学水平和多个自旋多重度下对该团簇进行结构优化并分析。结果表明：团簇Co_nMoS共有21种稳定构型;通过对NPA （自然布居分析,natural population analysis）电荷、静电势、亲电指数、电离势、光学电负性和折射率等分析得出,金属原子有高概率失去电子,非金属原子相对更容易得到电子,团簇Co₅MoS中的构型5a在最稳定构型中有高的得失电子能力、反应活性和折射率,Co和Mo原子易发生亲核反应,S原子易发生亲电反应;对该团簇自旋布居数、原子磁矩、轨道磁矩和态密度分析发现,该团簇磁性主要由Co原子的d轨道提供,且团簇Co₃MoS表现出了比其它尺寸团簇更为稳定和优异的磁性。最终得出团簇Co₃MoS在磁性方面有较好的表现且构型5a在活性和光学领域有一定的潜力。     

(AB)8(AB=BN，AlP，GaAs，InSb)团簇环状结构与性质的密度泛函理论研究

用杂化密度泛函B3LYP方法研究了(AB)₈(AB=BN，AlP，GaAs，InSb)团簇环形结构的平衡几何构型、电子结构、振动特性以及极化率。计算结果表明，(AB)₈团簇的双层环状结构中，每个A(B)原子都与3个B(A)原子成键，且Ⅴ族元素的原子比Ⅲ族元素的原子更接近团簇中心，(BN)₈、(AlP)₈、(GaAs)₈、(InSb)₈的平均极化率依次增大，IR和Raman谱峰发生红移。另外，讨论了热力学稳定性和动力学稳定性的变化。     

Pd(Cu)在MgO(100)表面吸附CO和O2的理论研究

采用固体镶嵌势能模型和DFT/B3LYP方法研究了在Pd/MgO和Cu/MgO表面吸附CO和O₂分子的电子性质. 计算结果表明, 在完美MgO(100)表面Pd原子对CO和O₂的吸附能分别为206.5和84.8 kJ/mol, 因此可知Pd原子更容易吸附CO分子; 而当Pd原子附着于有氧缺陷的MgO表面时, 它对两种分子的吸附都非常弱. 相反, 附着于MgO表面的Cu原子对O₂分子的吸附更为有利, 其吸附能在140～155 kJ/mol之间. 研究结果还表明, 对于双分子吸附体系, 即CO＋CO, CO＋O₂, O₂＋O₂体系, 双分子之间的结合力可减小完美MgO表面上Pd原子与被吸附分子的相互作用, 使吸附能减少了46～96 kJ/mol. 而对于在MgO表面上的Cu原子, 只有O₂＋O₂ 体系使吸附能减少了大约50～71 kJ/mol.     

基于密度泛函理论分析团簇ConMoS(n=1~5)电子性质、光学性质及磁性

为了从理论层面深入探究团簇 Co_nMoS(n=1~5)的电子性质、光学性质及磁性,弄清其内在关联,依据拓扑学原理和密度泛函理论,在B3LYP/def2-TZVP量子化学水平和多个自旋多重度下对该团簇进行结构优化并分析。结果表明：团簇ConMoS共有21种稳定构型;通过对NPA(自然布居分析,natural population analysis)电荷、静电势、亲电指数、电离势、光学电负性和折射率等分析得出,金属原子有高概率失去电子,非金属原子相对更容易得到电子,团簇Co₅MoS中的构型5a在最稳定构型中有高的得失电子能力、反应活性和折射率,Co和Mo原子易发生亲核反应,S原子易发生亲电反应;对该团簇自旋布居数、原子磁矩、轨道磁矩和态密度分析发现,该团簇磁性主要由Co原子的d轨道提供,且团簇Co₃MoS表现出了比其它尺寸团簇更为稳定和优异的磁性。最终得出团簇Co₃MoS在磁性方面有较好的表现且构型5a在活性和光学领域有一定的潜力。     

Structural and electronic properties of tungsten trioxides: from cluster to solid surface

Geometries and electronic structures of WO₃(001) surface and a series of stoichiometric (WO₃) _n clusters (n = 1–6) have been systematically investigated using first-principles density functional calculations. Six possible reconstructured models of WO₃(001) surface with cubic phase are explored, and the most stable configuration is the \( (\sqrt 2 \times \sqrt 2 )R45^{\circ} \) surface. The main feature of WO₃(001) surface is that the top of valence band is dominated by the 2p states of the bridging oxygen atom, rather than the top terminal oxygen. By comparing the geometrical parameters, from the structural point of view, the W₃O₉ cluster can be used as the smallest molecular prototype of the WO₃ surface. However, in terms of the electronic structure, only until W₆O₁₈, the cluster begins to appear the electronic feature of the WO₃(001) surface. This may be due to the reason that the W₆O₁₈ cluster and the top layer of WO₃(001) surface show similar “stoichiometry” if we treat two kinds of oxygen atoms as different “elements”. In addition, for the chemical reactivity, using BH₃ as a probe molecule, the W₆O₁₈ cluster also bears general resemblance to the WO₃(001) surface, and the bridging oxygen atoms in two systems are the preferred sites for the nucleophilic reaction. Therefore, our results indicate that the W₆O₁₈ cluster with a spherical buckyball structure can be viewed as the smallest molecular model to understand the properties such as catalytic activity of WO₃(001) surface.     

O2 dissociative adsorption on the Cu‐, Ag‐, and W‐doped Al(111) surfaces from DFT computation

The O₂ adsorption and dissociation on M‐doped (M = Cu, Ag, W) Al(111) surface were studied by density functional theory. The adsorption energy of adsorbate, the average binding energy and surface energy of Al surface, and the doping energy of doping atom were calculated. All the doped atoms can be stably combined with Al atoms, while being slightly embedded in the surface to a certain depth. The TOP‐type surfaces are the most stable doped surfaces for O₂ adsorption, which is related to the orbital hybridization between the adsorbate and the surface atoms, the electronegativity, and the orbital energy level of the doping atoms. Moreover, the O atoms and doping atoms contribute significantly to the density of states (DOS), especially the O‐p orbital electrons and the d orbital electrons of doping atoms. The degree of O₂ dissociation is related to the doping atoms on Al surfaces, and the doping atoms actually resist the dissociation of O₂. W atoms have the best resistance effect on the O₂ dissociation as compared with Cu and Ag atoms, especially W‐1NN surface, which has both large barrier energy and reaction energy.     

A Novel Dimeric Polyoxotungstate Decorated by 3d-4f atoms: K4LaH[As2W20CuO67 (H2O)3]Cl2· 22.5H2O

A novel dimeric polyoxotungstate K₄LaH[As₂W₂₀CuO₆₇(H₂O)₃ ]Cl₂·22.5H₂O has been synthesized and characterized by IR, element analysis TG and cyclic voltammogram. The anion K₄LaH[As₂W₂₀CuO₆₇(H₂O) ₃]Cl₂·22.5H₂O can be characterized as two {As^IIIW₉O₃₃}⁹⁻ moieties linked via a {Cu(OH)}, a {W(H₂O)} and a {WO(H₂O)} group which total coordination numbers are respectively 5, 5, 6. An additional lanthanide atom connects the dimeric cluster via a W-O-La bond. The X-ray single crystal diffraction shows that it is in the triclinic system, space group P-1, with a = 12.287(6) ?, b = 20.197(1) ?,c=21.483(1)?,α = 62.584(8)°,β = 74.659(8)°,γ = 75.273(9)°,V = 4509(4)?³, Z = 2. To our known, the polyoxotungstate is the novel sandwich-type polyoxoanion, which is decorated by transition-metal and lanthanide atoms at the same time.     

Nucleation of CuGa Phases on the MgO(100) Surface

MSINDO calculations are presented for the coadsorption of Cu and Ga atoms as clusters and islands on the MgO(100) surface. The surface is simulated by a (8 × 8 × 3) Mg₉₆O₉₆ cyclic cluster. The relative number of Cu and Ga atoms was varied in order to understand the influence of copper rich and gallium rich phases. It was found that the copper atoms have a dominating influence on the structural arrangement in mixed phases. The adsorption sites of Cu and Ga atoms are preferably O atoms, but in mixed phases these sites are usually occupied by Cu atoms.     

Crystallographic shear in the Nb2O5WO3 and Ta2O5WO3 systems

Crystallographic shear (CS) phases occurring in the Nb₂O₅WO₃ and Ta₂O₅WO₃ systems near to WO₃ were characterized by X-ray diffraction and high-resolution transmission electron microscopy. The Nb₂O₅WO₃ samples were heated at 1600K. They contained ordered {104} and {001} CS planes and wavy CS which were composed of intergrowths of {104} and {001} CS segments. The composition range over which the {104} CS series extended was from (Nb,W)O_2.954 i.e., (Nb,W)₆₅O₁₉₂, to (Nb,W)O_2.942, i.e., (Nb,W)₅₂O₁₅₃. The composition range over which the {001} CS series extended was from (Nb,W)O_2.9375, i.e., (Nb,W)₁₆O₄₇ to (Nb,W)O_2.875, i.e., (Nb,W)₈O₂₃. The Ta₂O₅WO₃ samples were prepared at 1593, 1623, and 1672K. At lower temperatures ordered {103} CS phases were found, with a composition range extending between (Ta,W)O_2.960, i.e., (Ta,W)₅₀O₁₄₈, to (Ta,W)O_2.944, i.e., (Ta,W)₃₆O₁₀₆. At 1673K ordered {103} CS phases occurred, as did wavy CS composed of intergrowths of {103} and {104} CS segments.     

Synthesis of W‐doped TiO2 by low‐temperature hydrolysis: Effects of annealing temperature and doping content on the surface microstructure and photocatalytic activity

A series of tungsten‐doped Titania photocatalysts were synthesized using a low‐temperature method. The effects of dopant concentration and annealing temperature on the phase transitions, crystallinity, electronic, optical, and photocatalytic properties of the resulting material were studied. The X‐ray patterns revealed that the doping delays the transition of anatase to rutile to a high temperature. A new phase W_yTi_1‐yO₂ appeared for 5.00 wt% W‐TiO₂ annealed at 900 °C. Raman and diffuse reflectance UV–Vis spectroscopy showed that band gap values decreased slightly up to 700 °C. X‐ray photoelectron spectroscopy showed that surface species viz. Ti³⁺, Ti⁴⁺, O^2?, oxygen‐vacancies, and adsorbed OH groups vary depending on the preparation conditions. The photocatalytic activity was evaluated via the degradation of methylene blue using LED white light. The degradation rate was affected by the percentage of dopants. The best photocatalytic activity was achieved with the sample labeled 5.00 wt% W‐TiO₂ annealed at 700 °C.     

g-C3N4碳位掺杂电学及光学性质的分析

使用第一性原理研究了C位掺杂的g-C₃N₄的电学性质和光学性质,掺杂原子为B、P、S. g-C₃N₄有C1位和C2 位两种对称位碳原子,其中在C1 位上的掺杂易于C2 位,掺杂体系也较C2 位稳定. 相比于磷和硫在g-C₃N₄上的掺杂,硼掺杂最易于进行. 掺杂后体系的晶体结构之间差别较大,这与掺杂原子的大小以及电负性有关. 由轨道布居分布可知,掺杂后的硼、磷、硫原子价电子发生了变化,表明掺杂原子发生了杂化,与相邻原子以强的共价键相连. 掺杂原子与被取代的碳原子之间的价电子差异导致了能带的增加. 在原来的体系中,掺杂后的体系出现了一条新的能带,因此导致实际带隙下降,表明了掺杂后的体系导电性能增强. 对纯g-C₃N₄及掺杂g-C₃N₄的光学性质分析表明,g-C₃N₄的光学吸收主要在紫外光区,掺杂磷和硫后对g-C₃N₄的光吸收波长范围无改变,掺杂硼后的g-C₃N₄光吸收不再局限于紫外光区,而且延伸至可见光区和红外光区,并在红外光区有很强的吸收,表明g-C₃N₄掺杂硼后能大大地提高光催化效率. 电子能量损失光谱和光导率谱以及介电常数都佐证了上述观点.