A DFT study of adsorption and decomposition of nitroamine molecule on Mg(001) surface

The adsorption and dissociation mechanism of NH₂NO₂ on the Mg surface have been investigated by the generalized gradient approximation of density functional theory. Calculations employ a supercell (3 × 3 × 3) slab model and three-dimensional periodic boundary conditions. The strong attractive force between oxygen and Mg atoms induces the N–O bond of the NH₂NO₂ to decompose. The dissociated oxygen atoms and radical fragment of NH₂NO₂ oxidize readily Mg atoms. The largest adsorption energy is ?860.5 kJ/mol. The largest charge transfer is 3.76 e from surface Mg atoms to fragments of NH₂NO₂. The energy barriers of N–O bond dissociation are in a range of 11.6–36.5 kJ/mol. The adsorption energy of NH₂NO₂ on the Mg surface compensates the energy needed for the N–O bond dissociation.     

Methanol adsorption on the beta-Ga2O3 surface with oxygen vacancies: theoretical and experimental approach

Methanol adsorption on beta-Ga2O3 surface has been studied by Fourier transform infrared spectroscopy (FTIR) and by means of density functional theory (DFT) cluster model calculations. Adsorption sites of tetrahedral and octahedral gallium ions with different numbers of oxygen vacancies have been compared. The electronic properties of the adsorbed molecules have been monitored by computing adsorption energies, optimized geometry parameters, overlap populations, atomic charges, and vibrational frequencies. The gallia-methanol interaction has different behaviors according to the local surface chemical composition. The calculations show that methanol can react in three different ways with the gallia surface giving rise to a nondissociative adsorption, a dissociative adsorption, and an oxidative decomposition. The surface without oxygen vacancies is very reactive and produces the methanol molecule decomposition. The molecule is nondissociatively adsorbed by means of a hydrogen bond between the alcoholic hydrogen atom and a surface oxygen atom and a bond between the alcoholic oxygen atom and a surface gallium atom. Two neighbor oxygen vacancies on tetrahedral gallium sites produce the dissociation of the methanol molecule and the formation of a bridge bond between two surface gallium atoms and the methoxy group.     

Theoretical study of isomerism of compounds of CO and CO2 molecules with aluminum clusters Al13, Al12Ti,and Al12Ni

Structural characteristics, vibrational frequencies, and energies of isomers of compounds of CO and CO₂ molecules with the centered aluminum cluster Al₁₃ and its doped analogues Al₁₂M (M = Ti and Ni) have been calculated by the density functional theory method. For the Al₁₂MCO compounds, the most favor-able are two “fragment” isomers in which the C and O atoms are separated and built into the cluster cage, completing it to a 14-vertex polyhedron. In one of them, the C and O atoms are in the capping positions over adjacent trigonal MAl₂ faces; in the second isomer, there is the five-coordinate C* atom located in the center of a tetragonal MAl3 face and bound to the central Al atom through the long fifth bond. The “coordinated” isomers, in which the CO molecule is coordinated as a ligand to a cluster vertex, edge, or face, are unstable to removal of CO for Al₁₃CO, close in energy to the fragment isomers for Al₁₂NiCO, and considerably higher on the energy scale than the fragment isomers but remain stable to CO removal for Al₁₂TiCO. For the Al₁₂MCO₂ compounds, the most favorable is the fragment isomer in which both oxygen atoms are in the capping positions over adjacent faces and the C* atom is five-coordinate. The alternative oxo carbonyl isomer Al₁₂MO(CO) is close to the lowest-lying one in the case of M = Ni and is ～56 kcal/mol higher on the energy scale in the case of M= Ti. The less stable Al₁₂M(CO₂) isomer is the complex in which the CO₂ ligand is coordinated to an M-Al edge. According to calculations, addition of CO to Al₁₂MO and addition of CO₂ to Al₁₂M to form, respectively, Al₁₂MO(CO) and Al₁₂M(CO₂) can occur without noticeable barrier. The Al₁₂M(CO₂) and Al₁₂MO(CO) isomers are separated by a barrier, moderate for M = Ti (～16 kcal/mol) and small for M = Ni (～6 kcal/mol).     

Adsorption and decomposition of HMX and CL‐20 on Al(111) surface by DFT investigation

The adsorption and decomposition of HMX and CL‐20 molecules on the Al(111) surface were investigated by the generalized gradient approximation of density functional theory. The calculations employed a supercell (6 × 6 × 3) slab model and three‐dimensional periodic boundary conditions. The strong attractive forces between HMX (or CL‐20) molecule and Al atoms induce the breaking of N‐O and N‐N bonds in nitro group. Subsequently, the dissociated oxygen atoms, NO₂ groups, and radical fragments of HMX or CL‐20 oxidize the Al surface. The largest adsorption energy is ?1792.7 kJ/mol in B1, where CL‐20 decomposes into four O atoms and a CL‐20 fragment. With the number of the radical species in adsorption configurations increases, the corresponding adsorption energy increases greatly. We also investigated the decomposition mechanism of HMX and CL‐20 molecules on the Al(111) surface. The activation energies (E _a) for the dissociations A2, A3, B1, and B6 are 31.2, 47.9, 75.5, and 75.9 kJ/mol, respectively. Although CL‐20 is more sensitive than HMX in its gaseous state, the E _a of CL‐20 is higher than that of HMX when they adsorb and decompose on the Al(111) surface, which indicates that the HMX is even easier to decompose on Al(111) surface as compared with CL‐20. Copyright © 2016 John Wiley & Sons, Ltd.     

Adsorption of small molecules on helical gold nanorods: A relativistic density functional study

We study the adsorption of a variety of small molecules on helical gold nanorods using relativistic density functional theory. We focus on Au₄₀ which consists of a central linear strand of five gold atoms with seven helical strands of five gold atoms on a coaxial tube. All molecules preferentially adsorb at a single low‐coordinated gold atom on the coaxial tube at an end of Au₄₀. In most cases, there is significant charge transfer (CT) between Au₄₀ and the adsorbate, for CO and NO₂, there is CT from the Au₄₀ to adsorbate while for all other molecules there is CT from the adsorbate to Au₄₀. Thus, Au₄₀‐adsorbate can be described as a donor–accepter complex and we use charge decomposition analysis to better understand the adsorption process. We determine the adsorption energy order to be C₅H₅N >NO₂ > CO > NH₃ > CH₂?CH₂ > CH₂?CH? CHO > NO > HC?CH > H₂S > SO₂ > HCN > CH₃OH > H₂C?O > O₂ > H₂O > CH₄ > N₂. We find that the Au? C, Au? N, Au? S, and Au? O bonds are surprisingly strong, with clear implications for reactivity enhancement of the adsorbate. The Au? H bond is relatively weak but, for interactions via an H atom that is bonded to a carbon atom (e.g., CH₄), we find that there is large charge polarization of the Au? H? C moiety and partial activation of the inert C? H bond. Although the Au? S and Au? O bonds are generally weaker than the Au? C and Au? N bonds, we find that adsorption of H₂S or H₂O causes greater distortion of Au₄₀ in the binding region. However, the degree of distortion is small and the helical structure is retained, demonstrating the stability of the helical Au₄₀ nanorod under perturbations. © 2014 Wiley Periodicals, Inc.     

Density-functional study for the NOx (x = 1, 2) dissociation mechanism on the Cu(1 1 1) surface

Spin-polarized density functional theory calculation is employed to study the adsorption and dissociation of NO₂ molecule on Cu(1 1 1) surface. It is shown that the most favorable adsorption structure is the NO₂ (T,T-O-,O′-nitrito) configuration which has an adsorption energy of −1.49 eV. The barriers for step-wise NO₂ dissociation reaction, NO_2(g) → N_(a) + 2O_(a), are 1.05 (for O–N–O bond activation), and 2.08 eV (for N–O bond activation), respectively, and the entire process is 0.6 eV exothermic. The energetics of single N–O dissociation with and without the presence of N atom or O atom on the surface are also calculated. The results indicate that in the presence of O atom on Cu(1 1 1) surface would raise the N–O dissociation barrier, whereas in the presence of N atom decrease it. The interaction nature between adsorbates and substrate is analyzed by the local density of states (LDOS) calculation.     

Theoretical study of CO adsorption on gold/alumina substrates

Aiming to understand the role of the substrate in the adsorption of carbon monoxide on gold clusters supported on metal-oxides, we have started a study of that process on two different alumina substrates: an amorphous-like fully relaxed stoichiometric (Al2O3)20 cluster and the Al terminated (0001) surface of alpha-(Al2O3) crystal. In this paper, we present first principles calculations for the adsorption of one Au atom on both alumina substrate and the adsorption of Au8 on (Al2O3)20. Then, we study the CO adsorption on the minimum energy structure of these three different gold/alumina systems. A single Au adsorbs preferably on top of an Al atom with low coordination, the binding energy being higher in the case of Au/(Al2O3)20. CO absorbs preferably on top of the Au atom, but in the case of Au/(Al2O3)20, Au forms a bridge with the Al and O substrate atoms after CO adsorption. We find other stable sites for CO adsorption on the cluster but not on the surface. This result suggests that the Au activity toward CO may be larger for the amorphous cluster than for the crystal surface substrate. For the most stable Au8/(Al2O3)20 configuration, two Au atoms bind to Al and a O atoms respectively and CO adsorbs on top of the Au which binds to the Al atom. We find other CO adsorption sites on supported Au8 which are not stable for the free Au8 cluster.     

AlIII-Phthalocyanine: Darstellung,Eigenschaften und Kristallstruktur von Tetra(n-butyl)ammonium-trans-di(nitrito(O))phthalocyaninato(2−)aluminat(III)

Al^III Phthalocyanines: Synthesis, Properties, and Crystal Structure of Tetra(n-butyl)-ammonium-trans-di(nitrito(O))phthalocyaninato(2?)aluminate(III) [Al(Cl)Pc^2?] reacts with excess (ⁿBu₄N)NO₂ in dimethylformamide yielding less soluble blue tetra(n-butyl)ammonium-trans-di(nitrito(O))phthalocyaninato(2?)aluminate(III), (ⁿBu₄N)^trans[Al(ONO)₂Pc^2?], which crystallizes in the monoclinic space group C2/c (No. 15) with Z = 4. The Al atom is in the special position 4 d in the center of the Pc^2? ligand and the two nitrit ions are monodentate O-coordinated in a mutually trans arrangement to the Al atom. The Al? O and average Al? N_iso bond distances are 1.927(2) and 1.956 Å, respectively. The geometric data of the coordinated nitrite ion are: d(N? O) = 1.277(4) Å; d(N? O) = 1.221(4) Å; ?(O? N? O) = 114.3(3)°; ?(Al? O? N) = 121.3(2)°. The non-bonded O atoms are trans to the Al atom. The Pc^2? ligand is slightly ruffled. The UV-VIS-NIR spectra and the vibrational spectra are discussed.     

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.     

Ab initio study of NH3 and H2O adsorption on pristine and Na-doped MgO nanotubes

We have investigated, on the basis of density functional theory calculations, the structural and electronic properties of chemical modification of pristine and Na-doped MgONTs with NH₃ and H₂O molecules. We found that the NH₃ and H₂O molecules can be barrierlessly adsorbed on the Mg atom of the tube sidewall along with a charge transfer from the adsorbate to MgONT. The adsorption is chemical in nature with adsorption energies about ?22.3 and ?21.5 kcal/mol for H₂O and NH₃, respectively. The calculated density of state (DOS) shows that the chemical modification of MgONTs with these molecules can be generally classified as certain type of “harmless modification.” In other words, the electronic properties of the MgONT are little changed by the adsorption processes. The substitution of an Mg atom in the tube surface with an Na atom results in a semi-insulator to p-type semiconductor transition based on DOS analysis. It was also found that the doping process reduces the adsorption energies and the electronic properties of Na-doped MgONT is slightly more sensitive toward NH₃ and H₂O molecules, compared with the pristine one.     

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.     

Quantum-chemical modeling of the hydrogen spillover effect in the H/Pt/SnO<Subscript>2</Subscript> system

The hydrogen migration over the surface of platinum clusters applied to the tin dioxide crystal surface has been modeled by the density functional theory method within the generalized gradient approximation (GGA) under periodic conditions using a projector-augmented plane-wave (PAW) basis set with a pseudopotential. It has been demonstrated that the dissociative adsorption energy of a hydrogen molecule onto the Pt₁₉ cluster surface is 1.6 eV. The movement of the hydrogen atom over the cluster surface is ∼0.4 eV more favorable than in the bulk. The location of the hydrogen atom on the SnO₂ substrate is 1.62 eV more favorable than that on the upper face of the Pt₁₉ cluster. The barriers to migration of hydrogen atom over the surface of the platinum cluster applied to the SnO₂ surface are within 0.1–0.2 eV.     

苯分子与Si6O18H12和Al6O24H30团簇模型相互作用的理论研究

粘土矿已经被广泛用来去除有机物,修复和净化被石油碳氢化合物污染的土壤和地下水. 我们选择高岭石作为研究对象,构造了Si₆O₁₈H₁₂和Al₆O₂₄H₃₀两个团簇模型分别代表高岭石的硅氧层表面和铝氧层表面,在MP2/6-31G(d,p)//B3LYP/6-31G(d,p)的理论水平上系统地研究了气态下苯分子和高岭石团簇模型的相互作用. 并进一步分析了苯分子和高岭石表面相互作用的各种气态性质,比如：优化的几何构型、结构参数、吸附能、自然键轨道电荷分布、振动频率变化、静电势、电子密度性质(次级氢键的电子密度和拉普拉斯算符值)和电子密度差分等. 优化的几何构型表明苯分子吸附在高岭石表面的本质可能是次级氢键的形成. 其他性质的结果进一步验证了次级氢键的存在,并指出苯更倾向于吸附在高岭石的铝氧层表面,且苯环和铝氧层表面形成近似90°的夹角.     

Dissociative chemisorption of D2 on a Ni13 cluster

Selected characteristic results of a quasiclassical trajectory study of dissociative adsorption of a D₂ molecule on a Ni₁₃ cluster are presented. These include detailed probabilities as functions of the impact parameter and of the relative translational energy of D₂, and cross sections as functions of this energy. The roles of the initial rovibrational state of the D₂ molecule and of the initial temperature of the cluster are examined. The effect of freezing the cluster into a rigid geometry is tested.     

H2O and H2 interaction with ZnO surfaces: A MNDO,AM1, and PM3 theoretical study with large cluster models

We investigated the adsorption and heterolytic dissociation of H₂O and H₂ molecules on a (ZnO)₂₂ cluster corresponding to ZnO (0001), (000(OVERBAR)1), and (10(OVERBAR)10) surfaces using MNDO , AM 1 and PM 3 semiempirical procedures. The geometry of the adsorbed molecule has been optimized in order to analyze binding energies, charge transfer, and preferential sites of interaction. The adsorbed species interact most strongly when it is bonded to the twofold coordinated zinc atom of the cluster surface. The interaction of the H₂O molecule with the surface of ZnO has a charge transfer from H₂O to the surface ranging between 0.17 and 0.27 au. The neighboring atoms of the surface are the main receptors during the process of charge transfer. Our results indicate that there is a weak bonding of the hydrogen atom from OH with the oxygen surface atom that could produce the O(SINGLE BOND)H·O band. The interaction of the H₂ molecule with the surface is generally weak and only the PM 3 method yields a strong binding energy for this interaction. There is a charge transfer from the H₂ molecule to the surface. The chemisorption of H on oxygen atom of the surface transfer charge from the surface to the H. We also calculated the vibrational analyses for these interactions on ZnO surface and compared our results with available experimental data. © 1996 John Wiley & Sons, Inc.     

Single-point Attack of Two H2O Molecules towards a Lewis Acid Site on the GaAl12 Clusters for Hydrogen Evolution

The hydrogen evolution reaction (HER) of water with metallic aluminum-based materials provides an important way to address the global energy challenge; however, fundamental mechanism and reaction dynamics governing the chemical and electronic properties remain a debated research topic. Here we further study the HER mechanisms for water splitting on typical 13-atoms clusters, Al₁₂Ga and Al₁₃, by first-principles DFT calculations. We noted that the doping of a Ga atom into the Al₁₃ cluster could reduce the transition state barrier for H₂O dissociation on the metal cluster. Furthermore, it is interesting that the second water molecule prefers to adsorb on the same metal site giving rise to both thermodynamically and kinetically favorable reaction pathways. Based on the well-established complementary active sites (CAS) mechanism for metal cluster reactivity, we provide insights into the reaction dynamics of such metal clusters with two water molecules, which also sheds light on the Eley-Rideal and Langmuir-Hinshelwood mechanisms in surface science. Natural bond orbitals (NBO) analysis was conducted to evaluate the donor-acceptor charge-transfer interactions between the cluster and the nucleophilic reagent. These results gain a better understanding of the mechanism for water reacting with aluminum-based materials.     

Synthesis and crystal structure of New Amminecopper(II) Nitrates: [Cu(NH3)2](NO3)2 and [Cu(NH3)](NO3)2

[Cu(NH₃)₂](NO₃)₂ ( I ) and [Cu(NH₃](NO₃)₂ ( II ) were synthesized by interaction of molten NH₄NO₃ with [Cu(NH₃)₄](NO₃)₂ and Cu(NO₃)₂ · 3 H₂O, respectively, at 180 to 195°C for 24 hr. According to X-Ray single crystal analysis, I is orthorhombic (sp. gr. Pbca) with a = 5.678(1), b = 9.765(2), c = 11.596(2) Å, Z = 4, R = 0.060; II is monoclinic (sp. gr. P2₁/c) with a = 6.670(1), b = 8.658(2), c = 9.661(2) Å, β = 101.78(2)°, Z = 4, R = 0.027. In both structures, the nearest coordination environment of Cu is a slightly distorted square formed by N (from NH₃) and O atoms (from NO₃ groups). The structure of I consists of centrosymmetrical [Cu(NH₃)₂](NO₃)₂ molecules linked by hydrogen bonds. The Cu? N and Cu? O distances are 1.98 and 2.01 Å, respectively. In II , the Cu? N distance is 1.95 Å, the Cu? O distances are 1.96, 2.02, and 2.03 Å. The [CuO₃NH₃] squares are connected by NO₃ bridges into zigzag chains, which are linked into layers by longer Cu? O interactions (2.31 Å). Obviously, the layers are additionally strengthened and held together by hydrogen bonds.     

Density functional study of H2 molecule and H atom adsorption on α‐U(001) surface

Density functional theory method has been employed to investigate the adsorption of H₂ molecule and H atom on α‐U(001) surface. There exist four initial sites [top (A), triangle‐center (B), long‐bridge (C), and short‐bridge (D)] for H₂ and H atom adsorptions on α‐U(001) surface. The E_ads (adsorption energy) values on the top sites of H₂‐U(001) configurations are around ?0.666 eV, and H₂ molecule has been elongated but not broken into H atoms. For the other three sites, the E_ads values are around ?1.521 eV. The long‐bridge site is the most reactive site for H₂ decomposing. For the H‐U(001) configurations, the E_ads are around ?2.904 eV. Top site and short‐bridge site are the most reactive sites for the H atom react on the α‐U(001) surface. Our work reveals that the different reactive sites play discrepant effects on hydrogenation process. Geometric deformations, diffusion paths, and partial density of states of H₂‐U(001) and H‐U(001) configurations have also been analyzed. Copyright © 2016 John Wiley & Sons, Ltd.     

Facial dissociations of water molecules on the outside and inside of armchair single-walled silicon nanotubes: theoretical predictions from multilayer quantum chemical calculations

The possible reaction pathways of dissociative adsorption of a single water molecule on the sidewalls of armchair (n, n) (n?=?4?C10) single-walled silicon nanotubes (SWSiNT) have been investigated by the multilayer models. Both the simplified fragment embedding and ONIOM calculations were carried out to study the diameter dependence of reactivity for the dissociation of water on SWSiNTs. The active fragments with different cluster sizes, such as Si₁₆H₁₀, Si₃₀H₁₆, and Si_10mH_4m (m?=?4?C10), were used for the multilayer calculations. The employment of the medium-sized Si₃₀H₁₆ cluster is able to reach a good balance between the computational efficiency and accuracy for the large-sized reaction system. In comparison with those full B3LYP/LANL2DZ calculations for Si(4,4) and Si(5,5) nanotubes, the approximate multilayered models can give reasonable predictions on the optimized geometries, activation energies, and exothermic energies with significant reduction in computational cost. The external complexes of the dissociative adsorption of H₂O on SWSiNTs were predicted to be more stable than those internal complexes. The convex surfaces of SWSiNTs were also more reactive to H₂O with the smaller activation barrier energies (10?C13?kcal/mol) than those (15?C22?kcal/mol) on the concave side. Both the activation barriers and exothermic energies of dissociative adsorptions of H₂O on the internal (external) sidewalls of armchair SWSiNT were found to be insensitive to the tube curvature. The passivation of the outer surface and the removal of water molecules may be crucial for the experimental preparation of the single-walled silicon nanotubes.     

First‐principles calculations of oxygen adsorption on the Ti3Al (0001) surface

Adsorption energies and density of states for O atoms adsorption on the Ti₃Al (0001) surface have been calculated using first‐principles calculations based on density functional theory. It is found that the order of O atom adsorption on the Ti₃Al (0001) surface is associated with the adsorption energy as well as the distance of O atoms because of the interaction. The adsorption energy mainly depends on the bond number and bond strength between O and Ti atoms, and the adsorption site with rich‐Ti surface (H_I and HCP_Al) is first priority. The adsorption energy decreases with the increase of the oxygen coverage because of the characteristics of the valence d‐orbitals of transition metals surface. Furthermore, the density of states indicates that the hybridization peak of O and Ti atoms is mainly from the contribution of Ti 3d‐ and O 2p‐orbitals, and the hybridization peak of O and Al atoms from the contribution of Al 2p‐ and O 2p‐orbitals. Copyright © 2016 John Wiley & Sons, Ltd.