Theoretical study of small Mo clusters and molecular nitrogen adsorption on Mo clusters

This paper studies the small molybdenum clusters of Mo_n (n=2--8) and their adsorption of N₂ molecule by using the density functional theory (DFT) with the generalized gradient approximation. The optimized structures of Mo_n clusters show the onset of a structural transition from a close-packed structure towards a body-centred cubic structure occurred at n=7. An analysis of adsorption energies suggests that the Mo₂ is of high inertness and Mo₆ cluster is of high activity against the adsorption of N₂. Calculated results indicate that the N₂ molecule prefers end-on mode by forming a linear or quasi-linear structure Mo--N--N, and the adsorption of nitrogen on molybdenum clusters is molecular adsorption with slightly elongated N--N bond. The electron density of highest occupied molecular orbital and lowest unoccupied molecular orbital, and the partial density of states of representative cluster are also used to characterize the adsorption properties of N₂ on the sized Mo_n clusters.     

A density functional theory study on the adsorption of CO and O₂ on Cu-terminated Cu₂O（111） surface

The adsorptions of CO and O2 molecules individually on the stoichiometric Cu-terminated Cu2O(111) surface are investigated by first-principles calculations on the basis of the density functional theory.The calculated results indicate that the CO molecule preferably coordinates to the Cu2 site through its C atom with an adsorption energy of -1.69 eV,whereas the O2 molecule is most stably adsorbed in a tilt type with one O atom coordinating to the Cu2 site and the other O atom coordinating to the Cu1 site,and has an adsorption energy of -1.97 eV.From the analysis of density of states,it is observed that Cu 3d transfers electrons to 2π orbital of the CO molecule and the highest occupied 5σ orbital of the CO molecule transfers electrons to the substrate.The sharp band of Cu 4s is delocalized when compared to that before the CO molecule adsorption,and overlaps substantially with bands of the adsorbed CO molecule.There is a broadening of the 2π orbital of the O2 molecule because of its overlapping with the Cu 3d orbital,indicating that strong 3d-2π interactions are involved in the chemisorption of the O2 molecule on the surface.     

A density functional theory study on the adsorption of CO and O2 on Cu-terminated Cu2O （111） surface

The adsorptions of CO and 02 molecules individually on the stoichiometric Cu-terminatcd Cu20 （111） surface are investigated by first-principles calculations on the basis of the density functional theory. The calculated results indicate that the CO molecule preferably coordinates to the Cu2 site through its C atom with an adsorption energy of-1.69 eV, whereas the 02 molecule is most stably adsorbed in a tilt type with one O atom coordinating to the Cu2 site and the other O atom coordinating to the Cul site, and has an adsorption energy of -1.97 eV. From the analysis of density of states, it is observed that Cu 3d transfers electrons to 2π orbital of the CO molecule and the highest occupied 5σ orbital of the CO molecule transfers electrons to the substrate. The sharp band of Cu 4s is delocalized when compared to that before the CO molecule adsorption, and overlaps substantially with bands of the adsorbed CO molecule. There is a broadening of the 2π orbital of the 02 molecule because of its overlapping with the Cu 3d orbital, indicating that strong 3d-2π interactions are involved in the chemisorption of the 02 molecule on the surface.     

Structural Stabilities of Ordered Arrays of Nb4 Clusters on NaCI（IO0） Surface

Adsorption of ordered （2 × 2） arrays of Nb4 clusters on the insulating surface of NaCI（100） is studied by the first-principles calculations within the density functional theory. The calculations on the relaxed geometries and cohesive energies show that both the tetrahedron and quadrangle-Nb4 can be stably adsorbed on this substrate, which may have important applications. The adsorption of quadrangle-Nb4 on the NaCl（100） surface is more stable than that of tetrahedron-Nb4. Both the Nb4 clusters studied and a single Nb atom prefer the top site of the Cl atom in the NaCl（100） surface. Electronic structure analysis suggests that the interactions between the Nb4 clusters and the substrate are weak.     

Structural,electronic,and magnetic properties in FeAlAu_n(n=1–6)clusters:A first-principles study

The geometries,electronic and magnetic properties of the trimetallic clusters Fe Al Aun(n = 1–6) are systematically investigated using density functional theory(DFT).A number of new isomers are obtained to probe the structural evolutions.All doped clusters show larger relative binding energies than pure Aun+2partners,indicating that doping with Fe and Al atoms can stabilize the Aun clusters.The highest occupied molecular orbital–lowest unoccupied molecular orbital(HOMO–LUMO) gaps,vertical ionization potentials and vertical electron affinities are also studied and compared with those of pure gold clusters.Magnetism calculations demonstrate that the magnetic moments of Fe Al Aun clusters each show a pronounced odd–even oscillation with the number of Au atoms.     

Dissociative Chemisorption of an H2（v,j） Molecule on Rigid Ni （100） Surface： Dependence on Surface Topologies and Initial Rovibrational States of the Molecules

The H2(v,j) Ni(100) collision system has been studied to understand the effects of the surface sites and initial rovibrational states of the molecule on molecule-surface interactions, by a quasiclassical molecular dynamic simulation method. Dissociative adsorption of an H2 molecule on the rigid Ni(100) surface is investigated at topologically different three sites of the surface. Interaction between the molecule and Ni surface was described by a London-Eyring-Polani-Sato (LEPS) potential. Dissociative chemisorption probabilities of the H2(v, j) molecule on various sites of the surface are presented as a function of the translation energies between 0.001-1.0eV. The probabilities obtained at each collision site have unique behaviour. At lower collision energies, indirect processes enhance the reactivity, effects of the rotational excitations and impact sites on the reactivity are more pronounced. The results are compared with the available studies. The physical mechanisms underlying the results and quantum effects are discussed.     

First Principles Study of Adsorption and Reaction of CO on SrTiO3 （100） Surface： the Role of Surface Oxygen Vacancies

The adsorption and reaction of CO on SrTiO3 （100） surface with and without surface oxygen vacancy are investigated by the first-principles calculation based on the density functional theory. The calculated results reveal that the oxygen vacancy site prefers to the activation of the C-O bond. The adsorption energies increase to 1.0855 and 0.3245eV for defect-CO and defect-OC orientations, respectively. Particularly the C-O bond is elongated by about 0.1285 ？ in the defect-OC orientation compared with that in the Ti-OC one without surface oxygen vacancies. There is predominantly a chemisorption mechanism between the CO molecule and the surface in the defect-CO orientation.     

Na decorated B6 cluster and its hydrogen storage properties

The structures and hydrogen storage properties of sodium atoms decorated B6 clusters are investigated by the B3LYP method with a 6-311＋G （d, p） basis set. For NamB6 （m = 1-3） clusters, Na atoms are always inclined to separate far enough from each other and not cluster together on a B6 cluster surface so that each Na atom has sufficient space to bind hydrogen molecules. The hydrogen storage gravimetric density of a two Na atoms decorated B6 cluster is 17.91 wt% with an adsorption energy per H2 molecule （AAE/H2） of 0.6851 kcal.mo1^-1. The appropriate AAE/H2 and preferable gravimetric density of the two Na atoms decorated B6 cluster complex indicate that it is feasible for hydrogen storage application in ambient conditions.     

Interaction of Methane with Single-Walled Carbon Nanotubes： Role of Defects,Curvature and Nanotubes Type

We investigate the interaction of single-walled carbon nanotubes （SWCNTs） and methane molecule from the first principles. Adsorption energies are calculated, and methane affinities for the typical semiconducting and metallic nanotubes are compared. We also discuss role of the structural defects and nanotube curvature on the adsorption capability of the SWCNTs. We could observe larger adsorption energies for the metallic CNTs in comparison with the semiconducting CNTs. The obtained results for the zig zag nanotubes with various diameters reveal that the adsorption energy is higher for nanotubes with larger diameters. For defected tubes the adsorption energies are calculated for various configurations such as methane molecule approaching to the defect sites pentagon, hexagon, and heptagon in the tube surface. The results show that the introduce defects have an important contribution to the adsorption mechanism of the methane on SWNTs.     

Adsorption behavior of triphenylene on Ru(0001) investigated by scanning tunneling microscopy

As a representative of small aromatic molecules, triphenylene(TP) has markedly high carrier mobility and is an ideal precursor for building graphene nanostructures. We mainly investigated the adsorption behavior of TP molecules on Ru(0001) by using scanning tunneling microscopy(STM). In submonolayer regime, TP molecules are randomly dispersed on Ru(0001) and the TP overlayer can be thoroughly dehydrogenated and converted into graphene islands at 700 K. Due to weak interaction between TP molecules and graphene, the grooves formed among graphene islands have confinement effect on TP molecules. TP adopts a flat-lying adsorption mode and has two adsorption configurations with the 3-fold molecular axis aligned almost parallel or antiparallel to the ■ direction of the substrate. At TP coverages of 0.6 monolayer(ML)and 0.8 ML, the orientational distributions of the two adsorption configurations are equal. At about 1.0 ML, we find the coexistence of locally ordered and disordered phases. The ordered phase includes two sets of different superstructures with the symmetries of ■R23.41° and p(4 × 4), respectively. The adsorption behavior of TP on Ru(0001) can be attributed to the delicate balance between molecule–substrate and molecule–molecule interactions.     

Large adsorption energies for CO on Sc_n(n=2-8,13) nanoclusters

In order to seek a transition metal cluster with high ability to adsorb CO molecule, the author performs a density function theory calculation on COSc_n(n= 2–8, 13) clusters. The results demonstrate that COSc_n(n = 2–8, 13) clusters have the large adsorption energies of which the values are over 3.6 e V, and the elongations of C–O bond length exceed 20%in most calculated sizes. Adsorbing CO contributes to the improvement of the chemical activity, but reduces the magnetic moment of corresponding Scn cluster.     

First-principles study of hydrogen adsorption on titanium-decorated single-layer and bilayer graphenes

The adsorption of hydrogen molecules on titanium-decorated （Ti-decorated） single-layer and bilayer graphenes is studied using density functional theory （DFT） with the relativistic effect. Both the local density approximation （LDA） and the generalized gradient approximation （GGA） are used for obtaining the region of the adsorption energy of H2 molecules on Ti-decorated graphene. We find that a graphene layer with titanium （Ti） atoms adsorbed on both sides can store hydrogen up to 9.51 wt% with average adsorption energy in a range from -0.170 eV to 0.518 eV. Based on the adsorption energy criterion, we find that chemisorption is predominant for H2 molecules when the concentration of H2 molecules absorbed is low while physisorption is predominant when the concentration is high. The computation results for the bilayer graphene decorated with Ti atoms show that the lower carbon layer makes no contribution to hydrogen adsorption.     

Density functional study on the bimetallic Ti_mZr_n(n+m ≤ 5) clusters and their interactions with H_2

Equilibrium geometries, stabilities, and electronic properties of small Ti_mZr_n(n + m ≤ 5) clusters were investigated using the density functional method. The ground states were determined, and it was found that the larger clusters and those consisting of more Zr atoms are more stable. The electronic properties of the clusters were discussed based on HOMO-LUMO gaps, vertical ionization potentials(VIP), and vertical electron affinities(VEA). Furthermore, we studied the interactions between those clusters and molecular hydrogen, and found that in all the cases dissociative chemisorptions occurred. According to the chemisorption energies, the pure Zr clusters are relatively more active towards H_2 when compared with the others except Ti_3Zr, which shows the highest activity. The magnetic moments of Ti_mZr_n and Ti_mZr_nH_2 were also compared, and the results show that the hydrogenated clusters have the same or decreased total magnetic moments with respect to the bare clusters except for Ti_3Zr_2.     

Two-photon absorption properties of aggregation systems on the basis of (E)-4-(2-nitrovinyl) benzenamine molecules

Aggregation effect caused by the intermolecular hydrogen-bonding interactions on two-photon absorption properties of (E)-4-(2-nitrovinyl) benzenamine molecules is studied at a hybrid density functional level. The geometry optimization studies indicate that there exist two probable conformations for the dimers and three for the trimers. A strong red-shift of the charge-transfer states is shown. The two-photon absorption cross sections of the molecule for certain conformations are greatly enhanced by the aggregation effect, from which a ratio of 1.0:2.6:3.6 is found for the molecule and its dimer and trimer with nearly planar structures. Namely, a 30 or 20 percent increase of the two-photon absorption cross section is observed.     

CO adsorption on small Aun（n=1-7） clusters supported on a reduced rutile TiO2（110） surface:a first-principles study

CO adsorption on small Au n(n = 1-7) clusters which are supported by a partially reduced rutile TiO 2(110) surface has been investigated by the first-principles method.The low coordinated sites of Au clusters are favorable for CO adsorption.CO-Au n-TiO 2 system displays surface magnetism.There is a strong interaction between the adsorbed CO molecule and the supported Au clusters.     

Geometric,stable and electronic properties of Aun-2Y2（n=3-8） clusters

Employing first-principles methods,based on the density function theory,and using the LANL2DZ basis sets,the ground-state geometric,the stable and the electronic properties of Aun-2Y2 clusters are investigated in this paper.Meanwhile,the differences in property among pure gold clusters,pure yttrium clusters,gold clusters doped with one yttrium atom,and gold clusters doped with two yttrium atoms are studied.We find that when gold clusters are doped by two yttrium atoms,the odd-even oscillatory behaviours of Aun-1Y and Aun disappear.The properties of Aun-2Y2 clusters are close to those of pure yttrium clusters.     

Geometries, stabilities, and electronic properties of Be-doped gold clusters: a density functional theory study

We have systematically investigated the geometrical structures, relative stabilities and electronic properties of small bimetallic AunBe (n = 1, 2, . . . , 8) clusters using a density functional method at BP86 level. The optimized geometries reveal that the impurity beryllium atom dramatically affects the structures of the Aun clusters. The averaged binding energies, fragmentation energies, second-order difference of energies, the highest occupied-lowest unoccupied molecular orbital energy gaps and chemical hardness are investigated. All of them exhibit a pronounced odd-even alternation, manifesting that the clusters with even number of gold atoms possess relatively higher stabilities. Especially, the linear Au2Be cluster is magic cluster with the most stable chemical stability. According to the natural population analysis, it is found that charge-transferring direction between Au atom and Be atom changes at the size of n = 4.     

First Principle Calculation on Aun Ag2 (n = 1 ～ 4) Clusters

The first-principles method based on density-functional theory is used to investigate the geometries of the lowest-lying isomers of Aun Ag2 (n = 1 ～ 4) clusters. Several low-lying isomers are determined, and many of them in electronic configurations with a high spin multiplicity. The stability trend of Ag-doped Aun clusters is compared to that of pure Aun clusters. Our results indicate that the inclusion of two Ag atoms in the clusters lowers the cluster stability, indicating higher stability as the structures grow in size. The bigger energy difference between the Aun and Aun Ag2 curves as the structures grows in size. This information will be useful to understanding the enhanced catalytic activity and selectivity gained by using silver-doped gold catalyst.     

Influence of Pb adatom on adsorption of oxygen molecules on Pb(111) surface: a first-principles study

Using first-principles calculations, we systematically study the influence of Pb adatom on the adsorption and the dissociation of oxygen molecules on Pb(111) surface, to explore the effect of a point defect on the oxidation of the Pb(111) surface. We find that when an oxygen molecule is adsorbed near an adatom on the Pb surface, the molecule will be dissociated without any obvious barriers, and the dissociated O atoms bond with both the adatom and the surface Pb atoms. The adsorption energy in this situation is much larger than that on a clean Pb surface. Besides, for an adsorbed oxygen molecule on a clean Pb surface, a diffusing Pb adatom can also change its adsorption state and enlarge the adsorption energy for O, but it does not make the oxygen molecule dissociated. And in this situation, there is a molecule-like PbO2 cluster formed on the Pb surface.     

Density functional theory study of MgnNi2 （n=1-6） clusters

The geometries of Mg n Ni 2(n = 1-6) clusters are studied by using the hybrid density functional theory(B3LYP) with LANL2DZ basis sets.For the ground-state structures of Mg n Ni 2 clusters,the stabilities and the electronic properties are investigated.The results show that the groundstate structures and symmetries of Mg clusters change greatly due to the Ni atoms.The average binding energies have a growing tendency while the energy gaps have a declining tendency.In addition,the ionization energies exhibit an odd-even oscillation feature.We also conclude that n = 3,5 are the magic numbers of the Mg n Ni 2 clusters.The Mg 3 Ni 2 and Mg 5 Ni 2 clusters are more stable than neighbouring clusters,and the Mg 4 Ni 2 cluster exhibits a higher chemical activity.