H2O在Cu(100)表面吸附的从头算研究

用量子化学从头计算方法,以原子簇Cu₅为模拟表面,研究了水在Cu(100)面上不同吸附位的吸附情况,结果表明:水分子通过氧原子与表面成键,顶位是其最佳吸附位,吸附能约为70kJ/mol,平衡距离为0.213nm,氢原子远离表面.在氧原子不加极化函数时,水分子的二次轴垂直于表面时能量最低,但倾斜至50°所需能量仅在10kJ/mol以内.当考虑O原子d轨道的影响时,水分子倾斜时能量较低,得到了与实验相符的吸附构型.另外还研究了表面电荷对吸附体系的影响,结果表明:表面带正电荷时,水与表面间的相互作用增强,水上所转移电荷增多,Cu-O间平衡距离减小;表面带负电荷时,情况与之相反,且氢原子靠近表面时,势能曲线有最低点.     

H2O在Al(111)表面吸附的量子化学研究

用量子化学从头算方法,以原子簇Al10模拟表面,研究了水在Al(111)表面上不同吸附位的吸附情况,计算得到了稳定的吸附构型和结合能·结果表明：顶位是其最佳吸附位,而且水在表面能以两种取向被吸附,距表面较远时,H端靠近表面,然后跨过一能垒到达最佳吸附位,此时氧端靠近表面·在吸附过程中,水向表面转移电荷,导致表面功函降低·在氧原子不加极化函数时,水分子的二次轴垂直于表面时能量最低;当考虑水中氧的d轨道的影响时,水分子倾斜吸附时能量较低,得到与实验相符的吸附构型。另外还研究了表面电荷对吸附体系的影响,结果表明：表面电荷能使水分子定向,带正电荷时,氧端朝向表面,水分子与表面间平衡距离缩短,吸附作用较强;带负电荷时,水分子氢端朝向表面,吸附的平衡距离较长,吸附能较小。     

为什么水在金属表面的吸附构型是倾斜的——水在铜、铝表面吸附的量子化学计算

用量子化学从头算方法,分别以原子簇Cu5、Al4、Al10模拟Cu(100)和Al(111)表面,在不同基组水平上,计算了水在两种金属表面上倾斜吸附的势能面,结果表明：当计算基组中不含氧原子的d轨道时,得到水分子在金属表面垂直吸附的构型,这与实验结果不符;当水中氧原子加极化函数时,水分子倾斜吸附时能量较低,得到与实验相符的吸附构型。这说明水中氧原子d轨道在计算中起着关键作用,在成键过程中有着重要影响。     

CH3O和CO在Pd(111)表面偶联反应机理的理论研究

采用DMol³程序包中的GGA-PW91方法, 结合周期平板模型, 对CH₃O和CO在Pd(111)表面的反应进行了系统研究. 计算结果表明, 吸附在Pd(111)表面顶位上的CO分子中C原子所带正电荷最多, 容易与亲核试剂反应, 化学吸附能稍低, 有利于在表面上移动发生亲电插入反应; CH₃O 在Pd(111)表面fcc穴位吸附稳定, O原子上所带的负电荷较多, 易被亲电试剂进攻. 过渡态搜索表明, Pd(111)表面顶位上的CO与fcc穴位上CH₃O反应生成CH₃OOC的为放热反应, 反应能垒较低, 有利于偶联反应的进行.     

NO分子在金表面吸附的理论研究

气体分子在过渡族金属表面吸附是异相催化过程中的一个重要步骤.研究其在金属表面的吸附特性是了解其催化性能的基础,多年来一直是表面科学领域的研究热点.理论研究在解释吸附机理、实验现象以及证实实验结论的可靠性方面发挥着越来越重要的作用.本文使用密度泛函理论(DFT)研究了NO分子在中性及带正、负电荷的Au(111),Au(100),Au(310)和Au/Au(111)表面的吸附行为.研究结果表明,NO倾斜地吸附在金表面.在这种吸附构型中,Au原子的dz2轨道和NO分子的2π*轨道对称性匹配,并达到最大重叠.中性及带正、负电荷的Au(111),Au(100),Au(310)和Au/Au(111)表面不同吸附位对NO的反应活性不同,NO易吸附于各个金表面的顶位.计算结果显示,NO分子在Au(111)面几乎不吸附,而在Au/Au(111)的吸附能高达0.89eV.对表面金原子d态电子分波态密度分析表明,金表面对NO分子的吸附活性随着金原子配位数的减少而增强,这是由于低配位数的金原子的d态电子更靠近费米能级.当金表面增加或减少一个电子时,金表面对NO的吸附能有明显变化.正电荷的金表面对NO吸附的活性比中性的表面活性高,而带...     

水在NanZSM-5型分子筛中吸附的研究: 分子模拟

利用分子动力学(MD)模拟退火的方法和巨正则系综Monte Carlo模拟方法(GCMC)研究了水在NanZSM-5型分子筛中的吸附行为, 计算结果与文献中报道的实验结果吻合较好. 在此基础上, 进一步预测了水在不同硅铝比的NanZSM-5型分子筛中的吸附性质, 计算结果显示: 分子筛骨架上的硅铝比会显著影响水分子的吸附量和吸附等温线, 随着硅铝比的降低, 水的吸附量增加; 水分子的吸附位置是在钠离子和铝原子的周围, 平均每个钠离子周围吸附4个水分子, 而当水的吸附量增大时, 水分子与分子筛骨架上的氧原子之间发生了氢键作用; 在吸附量相同的条件下, 水的吸附热随着硅铝比的降低而升高.     

NH4Y沸石分子筛上质子的运动(Ⅰ)——用CNDO/2法计算氨在HY沸石上的吸附热及质子在NH4Y内的迁移

用CNDO/2方法定量计算氨在HY(Si/Al=2.4)沸石上的吸附热,其值24.4kcal/mol与实验值符合较好。质子在表面与NH₃间迁移,有两个能量极小值;吸附时,质子从接近表面的极小迁移到接近NH₃极小时,要越过势垒9.40kcal/mol;反之要越过势垒11.9kcal/mol。400℃时,质子在表面与NH₃间跳动频率为1.92×10⁹sec^-1。NH₃吸附后,NH键长增加,加以质子迁移,导致NH₈上负电荷密度向沸石表面迁移,使H上的电子集居数减少,H更质子化。     

磺基甜菜碱两性表面活性剂的结构性质

用量子化学中的密度泛函理论, 在B3LYP/6-31＋G*水平上, 对十二烷基磺基甜菜碱分子进行了结构优化, 在分子水平上研究了两性表面活性剂与阳离子(Ca^2＋)、阴离子(Cl^－)之间的相互作用. 计算结果表明: 两性表面活性剂的负电荷中心采用2∶1型, 即极性头中两个氧原子与阳离子发生稳定结合|而正电荷中心采用侧方, 即N原子的两个亚甲基和一个甲基与阴离子发生稳定结合. 由于桥联亚甲基和α-亚甲基均带有一定数量的电荷, 因此两性表面活性剂中正负电荷中心需要根据亚甲基上电荷多少进行划分. 计算也发现, 表面活性剂尾链带有部分弱电荷, 使胶束内核带有了部分极性, 利于表面活性剂在溶液中的聚集, 此种极性介于烷烃油相和水相的极性之间.     

阴离子Gemini表面活性剂在油/水界面行为的分子动力学模拟

采用分子动力学方法研究了磺酸盐型阴离子Gemini表面活性剂在油/水界面的吸附行为, 考察了不同长度的连接基(Spacer)对表面活性剂在界面的聚集形态及界面性质的影响. 密度分布和微观结构信息显示, Gemini表面活性剂能在油/水界面形成单层膜结构. Gemini表面活性剂能使油/水界面的厚度显著增大, 并使界面形成能降低. 当连接基为6个碳时, 此类磺酸盐型Gemini表面活性剂的界面厚度最大, 形成的界面最稳定. 连接基长度对Gemini表面活性剂单层膜周围的水分子和Na⁺的吸附结构影响不大, 但是能影响水分子的扩散行为.     

吸附与润湿II.Triton X-100和Triton x-305在炭黑/水和炭黑/环己烷界面上的吸附层结构

测定了15℃和30℃时炭黑自水和环己烷中吸附非离子型表面活性剂TritonX-100和Triton X-305的等温线;计算了吸附过程的标准热力学函数;测定了石墨/水/环己烷和石墨/水/空气的接触角与表面活性剂浓度的关系, 分析所得结果,可得结论:在炭黑/水或石墨/水界面上,Triton型表面活性分子形成单分子吸附层,分子以憎水的iso-C8H17C6H4基团附着在表面,而以亲水的聚氧乙烯链伸入水相的方式取向;在炭黑/环已烷或石墨/环己烷界面上,分子是通过聚氧乙烯链吸附到表面上的,当浓度增加时分子在表面可能通过聚氧乙烯链间的相互作用而发生聚集,即可能形成表面反式胶团。     

Molecular dynamics simulations of electrolyte solutions at the (100) goethite surface

Molecular dynamics simulations of electrolyte solutions in contact with a neutral (100) goethite (alpha-FeOOH) surface were used to probe the structure of the mineral-water interface and gain insight into the adsorption properties of monovalent ions. Three electrolyte solutions were considered: NaCl, CsCl, and CsF. The electrolyte ions were chosen to cover a range of ionic sizes and affinities for the aqueous phase. The molecular dynamics simulations indicate the presence of a structured interfacial region resulting from the strong interaction of water with the mineral surface. The specific arrangement and preferred orientation of water that arise from this interaction create adsorption sites in the interfacial region, i.e., as far as 15 A away from the surface, and hence give rise to a strong correlation between the water and ion distributions. The structure of the hydrated ion, its effect on the water arrangement at the interface, and the strength of the ion-water bond are found to be key factors that determine the location and extent of ion adsorption at the interface. Additionally, in all simulations, we find a build up of positive charges near the surface due to cation adsorption, which is compensated by an accumulation of anions in the next few angstr?ms. This creates an excess of negative charges, which is in turn compensated by an excess of positive charges, and so on. As we modeled a neutral surface, the structure of the electrolyte distribution arises from the complex interplay of the interactions between the surface, water, and the electrolyte ions rather than from the need to neutralize a surface charge. In addition, our simulations indicate that the electrolyte distribution does not resemble that of a classical electrical double layer. Indeed, our calculations predict the presence of several condensed layers and oscillations in the net charge away from the surface.     

Solvent reorganization in electron and ion transfer reactions near a smooth electrified surface: a molecular dynamics study

Molecular dynamics simulations of electron and ion transfer reactions near a smooth surface are presented, analyzing the effect of the geometrical constraint of the surface and the interfacial electric field on the relevant solvation properties of both a monovalent negative ion and a neutral atom. The simulations show that, from the solvation point of view, ion adsorption is an uphill process due to the need to shed off the ion's solvation shell and displace water from the surface. Atom adsorption, on the other hand, has only a small barrier, related to the molecularity of the solvent. Both the electrostatic interaction of the ion with the solvent and the ion's solvent reorganization energy (the relevant parameter in the Marcus electron transfer theory) decrease as the surface is approached, whereas these parameters are not sensitive to the distance from the surface for the atom. This is a consequence of the importance of long-range electrostatic interactions for ion solvation and the importance of short-range interactions for atom solvation. The electric field either attracts or repels an ion to or from the surface, but the field has no influence on the solvent reorganization energy. By including the quantum-mechanical electron transfer between the metal surface and the ion/atom in solution in the MD simulation by using a model Hamiltonian, we calculated two-dimensional free energy surfaces for ion adsorption allowing for partial charge transfer, based on a fully molecular picture of ion solvation near the surface.     

SURFACE PROPERTIES OF SOME LOW MOLECULAR WEIGHT PROTEINS

Surface properties of four proteins having molecular weights less than 5,000 are reported at air/water and alumina/water interface at pH 7.0. Reversibility in the adsorption of these proteins at the alumina/water interface is tested. The adsorption on alumina/water interface has been found to be controlled by electrostatic interaction. Positive adsorption was obtained when protein and alumina surface had opposite charges and negative adsorption was obtained when both protein and surface had same charges. Of the four proteins reversibility in adsorption was observed with the one having the lowest molecular weight of 3100. The adsorption behavior apparently had no correlation with their surface hydrophobic!ty. Time dependent changes in air/water interfacial tension was observed for all the four proteins indicating time dependent loosening of compact protein structure and surface unfolding.     

氢原子在金属锂表面台阶附近吸附和表面扩散行为的ab initio研究

取Li7H和Li9H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ab initip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Li7H体系, 台阶面附近沿垂直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Li9H体系, 在Li7H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内何位置几无改变, 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。     

Study of a Solvated Adsorbed Gelatin Layer Using a Modified Force Microscope

The interaction energies between gelatin-coated surfaces at various electrolyte and pH conditions are reported. The surfaces are of glass and are negatively charged under all conditions used here. Gelatin is a polyampholyte, with an isoelectric pH (IEP) of approximately 4.9. At low pH the gelatin molecules have a net positive charge, and thus the polyampholyte tends to adsorb with a relatively flat conformation. As the pH is increased the strong attractive interaction between the surface and the polyampholyte decreases as more negative charges and then fewer positive charges appear on the polyampholyte, and so the gelatin extends away from the surface. On changing electrolyte concentrations after adsorption no effect was seen at the IEP, but the layer was observed to swell at more alkaline pHs. This is consistent with the net minimum charge situation on the polymer under these conditions. Changing the adsorption conditions was seen to have an effect, and this is attributed to the different affinities of the gelatin chain to the surface depending on the solution chemistry. Results obtained when the gelatin was initially adsorbed on one surface or two were similar, suggesting that the gelatin transfers rapidly from one surface to another. The importance of adsorption conditions as well as current conditions is discussed. Copyright 1999 Academic Press.     

应用理论计算研究MCM-22分子筛相邻酸性位上乙烯和苯的吸附

应用ONIOM计算方法研究了MCM-22分子筛超笼12元环上存在两个酸性位时的酸强度及其与骨架铝之间距离的关系,并研究了乙烯和苯分子吸附的规律.计算采用52T簇模型和B3LYP/6-31G**/MNDO方法.结果表明,存在两个酸性位且两个骨架铝之间间隔1个骨架硅时,酸强度比孤立的酸性位明显降低;当间隔的硅原子数增加时,酸强度呈上升趋势,间隔3个以上骨架硅时,其酸强度与孤立的酸性位几乎没有差别.对于乙烯的吸附,当两个骨架铝之间间隔1~4个骨架硅时,其吸附能几乎没有差别(31~35 kJ/mol);对于苯的吸附,当两个骨架铝之间间隔1个骨架硅时,其吸附能有所提高,因为两个桥羟基同时对苯分子产生氢键吸附作用.当两个骨架铝之间的距离增大时,苯的吸附能几乎相同(21~29 kJ/mol).若两个乙烯分子或苯分子同时吸附在双酸性位上,其吸附能与单个分子在孤立酸性位吸附时几乎没有差别.应用自然键轨道计算分析了吸附配合物的电子结构,进一步探明了乙烯和苯在分子筛酸性位上吸附的本质.     

Water monomer interaction with gold nanoclusters from van der Waals density functional theory

We investigate the interaction between water molecules and gold nanoclusters Au(n) through a systematic density functional theory study within both the generalized gradient approximation and the nonlocal van der Waals (vdW) density functional theory. Both planar (n = 6-12) and three-dimensional (3D) clusters (n = 17-20) are studied. We find that applying vdW density functional theory leads to an increase in the Au-Au bond length and a decrease in the cohesive energy for all clusters studied. We classify water adsorption on nanoclusters according to the corner, edge, and surface adsorption geometries. In both corner and edge adsorptions, water molecule approaches the cluster through the O atom. For planar clusters, surface adsorption occurs in a O-up/H-down geometry with water plane oriented nearly perpendicular to the cluster. For 3D clusters, water instead favors a near-flat surface adsorption geometry with the water O atom sitting nearly atop a surface Au atom, in agreement with previous study on bulk surfaces. Including vdW interaction increases the adsorption energy for the weak surface adsorption but reduces the adsorption energy for the strong corner adsorption due to increased water-cluster bond length. By analyzing the adsorption induced charge rearrangement through Bader's charge partitioning and electron density difference and the orbital interaction through the projected density of states, we conclude that the bonding between water and gold nanocluster is determined by an interplay between electrostatic interaction and covalent interaction involving both the water lone-pair and in-plane orbitals and the gold 5d and 6s orbitals. Including vdW interaction does not change qualitatively the physical picture but does change quantitatively the adsorption structure due to the fluxionality of gold nanoclusters.     

Calculation of henry constants for the adsorption of isomeric phenylenediamines on graphitized thermal carbon black

Henry constants for the adsorption of o- and p-phenylenediamines on the surface of graphitized thermal carbon black within the temperature range 433–479 K were calculated by the molecular statistical method. The parameters of the atom-atom potential function of intermolecular interaction between the nitrogen atom in aniline and isomeric phenylenediamines and the carbon atom of the basal face of graphite were determined. It was shown that an intramolecular H bond influenced the geometry and adsorption properties of o-phenylenediamine.