Density-functional theory study of the geometries,stabilities, and electronic properties of Au n Rb (n = 1–10) clusters: comparison with pure gold clusters

The density functional method with the relativistic effective core potential has been employed to investigate systematically the geometric structures, relative stabilities, growth-pattern behavior, and electronic properties of small bimetallic Au _n Rb (n?=?1–10) and pure gold Au _n (n?≤?11) clusters. For the geometric structures of the Au _n Rb (n?=?1–10) clusters, the dominant growth pattern is for a Rb-substituted Au _{n +1} cluster or one Au atom capped on a Au _{n –1}Rb cluster, and the turnover point from a two-dimensional to a three-dimensional structure occurs at n?=?4. Moreover, the stability of the ground-state structures of these clusters has been examined via an analysis of the average atomic binding energies, fragmentation energies, and the second-order difference of energies as a function of cluster size. The results exhibit a pronounced even–odd alternation phenomenon. The same pronounced even–odd alternations are found for the HOMO–LUMO gap, VIPs, VEAs, and the chemical hardness. In addition, about one electron charge transfers from the Au _n host to the Rb atom in each corresponding Au _n Rb cluster.     

All-electron relativistic calculation on Au5X (X = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) clusters

All-electron scalar relativistic calculations on Au₅X (X = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) clusters have been performed by using density functional theory with the generalized gradient approximation. Our calculation results indicate that all the lowest energy geometries of Au₅X clusters have planar structures; the doped X atoms prefer to occupy the fourfold coordination site. Except Au₅Fe, Au₅Co and Au₅Zn, for other clusters including pure Au₆ cluster, the HOMO are delocalized obviously with a contribution from all atoms in the cluster. On the contrary, the electron localization in Au₅Zn is very strong resulting in the least stability of this cluster. Au₅Cu cluster with six delocalized electrons being defined as magic number for two-dimensional system has the largest VIP and deepest HOMO energy level. With the substitution Au for X atoms, the metallicity of all Au₅X clusters is reinforced.     

Probing the structural,electronic and magnetic properties of small Au4M (M = Sc–Zn) clusters

Density-functional method PW91 has been selected to investigate the structural, electronic and magnetic properties of Au₄M (M =Sc–Zn) clusters. Geometry optimisations show that the M atoms in the ground-state Au₄M clusters favour the most highly coordinated position. The ground-state Au₄M clusters possess a solid structure for M = Sc and Ti and a planar structure for M = V–Zn. The characteristic frequency of the doped clusters is much greater than that of pure gold cluster. The relative stability and chemical activity are analysed by means of the averaged binding energy and highest occupied molecular orbital and lowest unoccupied molecular orbital energy gap for the lowest energy Au₄M clusters. It is found that the dopant atoms can enhance the thermal stability of the host cluster except for Zn atom. The Au₄Ti, Au₄Mn and Au₄Zn clusters have relatively higher chemical stability. The vertical detachment energy, electron affinity and photoelectron spectrum are calculated and simulated theoretically for all the ground-state structures. The magnetism calculations reveal that the total magnetic moment of Au₄M cluster is mainly localised on the M atom and vary from 0 to 5 μ_B by substituting an Au atom in Au₅ cluster with different transition-metal atoms.     

Ab initio calculation of the geometric,electronic and magnetic properties of neutral and anionic Au n Pd (n = 1–9) clusters

The ab initio method based on density functional theory at the B3PW91 level has been applied to study the geometric, electronic, and magnetic properties of neutral and anionic Au _n Pd (n?=?1–9) clusters. The results show that the most stable geometric structures adopt a three-dimensional structure for neutral Au₇Pd and Au₈Pd clusters, but for anionic clusters, no three-dimensional lowest-energy structures were obtained. The relative stabilities of neutral and anionic Au _n Pd clusters were analysed by means of the dependent relationships between the binding energies per atom, the dissociation energies, the second-order difference of energies, the HOMO–LUMO energy gaps and the cluster size n, and a local odd–even alternation phenomenon was found. Natural population analysis indicates the sequential transfer from the Pd atom to the Au _n frame in Au_1,2,3,5Pd and Au_2,3Pd^? clusters, and from the Au _n frame to the Pd atom in other clusters. Much to our surprise, irrespective of whether it is the total magnetic moment or the local magnetic moment, the magnetic moment presents an odd–even alternation phenomenon as a function of the cluster size n. The magnetic effects are mainly localized on the various atoms (Au or Pd) for different cluster size n.     

Stabilities,electronic and magnetic properties of Cu-doped nickel clusters: a DFT investigation

In this paper, we investigate the electronic and magnetic properties of Cu-doped nickel clusters by means of density functional theory. The stabilities of these clusters have also been studied in terms of the binding energies, second-order difference of energies, fragmentation energies and HOMO–LUMO energy gaps. The obtained results reveal that the N₄Cu, N₅Cu and Ni₇Cu clusters are found to be more stable that than all other clusters. Higher HOMO–LUMO gap was observed for Ni₅Cu cluster (2.265 eV), indicating its higher chemical stability. A half-metallic behaviour has also been observed for the Ni_nCu clusters, which suggests that these clusters can be employed as nanocatalysts for several catalytic processes, particularly for hydrogenation and dehydrogenation reactions. The magnetism calculations show that the magnetic moment is mostly located on the Ni atoms, and the contribution of the Cu atom to the total magnetic moment in the Ni_nCu clusters is very small. Furthermore, partial density of states analysis indicates that the 3d orbitals in Ni atoms are mostly responsible for the magnetic behaviour of these clusters, and the s orbitals have a very little contribution to the total magnetic moment.     

Adsorption sensitivity of pristine and Al- or Si-doped boron nitride nanoflake to COCl2: a DFT study

ABSTRACT

The adsorption of phosgene (COCl₂) on pristine, Al- and Si-doped boron nitride nanoflakes (BNNFs) is studied using density functional theory calculations. The adsorption energies of the most stable complexes, formed from interaction between COCl₂ and the pristine, Al- and Si-doped BNNFs are ?28.97, ?78.71 and ?171.60?kJ/mol at the M06-2X/6-31?+?G* level of theory, respectively. It is found that COCl₂ experiences a chemisorption interaction over the doped BNNFs, significantly altering its structure with respect to the gas-phase molecule. The COCl₂ adsorption can also induce a change in the HOMO–LUMO or SOMO–LUMO energy gap of the surface. In particular, the adsorption of COCl₂ is found to decrease the HOMO–LUMO energy gap of Al-doped BNNF by about 30%. It is suggested that the Al- or Si-doped BNNFs can be considered as a potential material for detecting toxic COCl₂.     

Theoretical study on the composition dependence of Ga8−nAsn (n=0-8) clusters

Using full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method, we have investigated the dependence of GaAs clusters with eight atoms on composition. It is found that the ground state structures for Ga-rich and As-rich clusters are cube structures. As the ratio between gallium atoms and arsenic atoms is close to one, structural distortion become increasingly severe, or even the clusters adopt other geometrical configurations as their ground state structures. The energy gap E_g between the highest-occupied molecular orbital (HOMO) and the lowest-unoccupied molecular orbital (LUMO), and the vertical electron affinity show a certain degree of even/odd alternation with cluster composition. Among nine Ga_8−nAs_n (n=0-8) clusters, only a few of clusters have different energy orders between the ionic and neutral isomers with large binding energy. Some ionic structures would change into other configurations due to severe structural distortion.     

Structural and electronic properties of full range of ternary PtmAunAgl (m + n+l = 5, 6 and 7) clusters: a density functional theory investigation

ABSTRACT

Density functional theory calculations have been carried out on ternary Pt_mAu_nAg_l clusters of low nuclearity (m?+?n+l?=?5, 6 and 7). Various properties including average bond distance, binding energy, mixing energy, ionisation potential, electron affinity, HOMO–LUMO gap and fragmental channel, are reported for the optimised structures. The variations of the calculated properties of the Pt_mAu_nAg_l clusters as a function of concentrations (i.e. all m-, n-, and l-values) are displayed by ternary diagrams. The geometric, energetic and electronic properties are sensitive to the composition and size of Pt_mAu_nAg_l clusters.     

Geometries,stabilities, electronic and magnetic properties of small PdnIr (n = 1–8) clusters from first-principles calculations

The geometrical structures, relative stabilities, electronic and magnetic properties of small Pd_nIr (n = 1–8) clusters have been systematically investigated using density functional theory at the B3PW91 level. The optimised geometries show that the lowest-energy structures of Pd_nIr clusters prefer a three-dimensional configuration. The relative stability of these clusters was examined by analysis of the binding energies per atom, fragmentation energies, the second-order difference of energies and the HOMO–LUMO energy gaps as a function of cluster size. The obtained results exhibit that the Pd₂Ir, Pd₃Ir and Pd₅Ir clusters are more stable than their neighbouring clusters. The energy gap of the Pd₂Ir cluster is the largest of all the clusters (2.258 eV). In addition, the charge transfers, vertical ionisation potentials, vertical electron affinities and chemical hardness were calculated and discussed. The magnetism calculations indicate that the total magnetic moment of Pd_nIr clusters is mainly localised on the iridium atom for Pd_1–6Ir clusters. Meanwhile, the 5d orbital plays the key role in the magnetic moment of the iridium atom.     

Copper hexadecafluoro phthalocyanine and naphthalocyanine: The role of shake up excitations in the interpretation and electronic distinction of high-resolution X-ray photoelectron spectroscopy measurements

We present the first high-resolution X-ray photoelectron core level spectra of bulk copper hexadecafluoro phthalocyanine (CuFPC) and naphthalocyanine (H₂NPC). The measurements have been performed in UHV onto samples grown in situ. A shake-up satellite assigned to a monopole on-site HOMO–LUMO molecular excitation has been evidenced in the F, C and N core-level spectra measured. In the case of the CuFPC, the shake-up is characteristic of the F atoms, of the four N atoms that are Cu bonded, and of the F- and N-bonded C atoms. The shake-up to main peak relative binding energy has been estimated to be 1.6 eV. In the case of H₂NPC, the outer benzenic C atoms do not show a satellite excitation, which instead is characteristic of the C and N atoms belonging to the inner porphyrin-like central ring of the molecule. The shake-up is less than 1 eV at higher binding energies from the main core line. The localisation of the HOMO level in the central structure of the molecule is confirmed by Hartree–Fock all-electron molecular orbital calculations performed on the metal-free phthalocyanine (H₂PC) and hexadecafluoro phthalocyanine (H₂FPC) molecules.     

碳掺杂硼氮纳米管电子场发射的第一性原理研究

对闭口硼氮纳米管（BNNT）顶层掺碳体系,运用第一性原理研究了电子场发射性能.结果表明,掺碳的BNNT体系电子结构变化显著;外电场愈强,体系态密度向低能端移动幅度愈大,且最高占据分子轨道（HOMO）/最低未占据分子轨道（LUMO）能隙愈小.体系态密度和局域态密度,HOMO和LUMO及其能隙分析一致表明,各种碳掺杂体系中C_eqBNNT的场发射性能最佳. 关键词： 硼氮纳米管 碳掺杂 第一性原理     

密度泛函理论计算内掺氢分子富勒烯H2＠C60及其二聚体的几何结构和电子结构

采用密度泛函理论中的广义梯度近似(generalized gradient approximation,简称GGA),对内掺氢分子富勒烯H₂＠C₆₀及其二聚体的几何结构和电子结构进行了计算研究.发现无论是在H₂＠C₆₀单体,还是在其二聚体中,氢倾向以分子形式存在于碳笼中心处,且在室温下氢分子可以做自由旋转.电子结构分析表明,氢分子掺入到C₆₀和C₁₂₀中,仅对距离费米能级以下-8eV至-5eV能级处有一定的贡献,其他能级的分布和能隙几乎没有变化. 关键词： 几何结构 电子结构 密度泛函     

Superatomic properties of transition-metal-doped tetrahexahedral lithium clusters: TM@Li14

ABSTRACT

The lowest energy structure of Li₁₅ cluster is a capped double centred square antiprism sharing a square face. Interestingly, when a lithium atom is substituted by a transition-metal atom TM (TM?=?Sc, Ti, V, Y, Zr, Nb, Hf, Ta and W), the lowest energy structure is found to be cage-like with a D_6d symmetry, where the outer cage is composed by fourteen lithium atoms with an endohedral transition-metal atom. The unique structures are confirmed by CALYSPO structure prediction method code and density-functional theory calculations. Superatomic properties are confirmed in all the D_6d clusters. Energy calculations predict that they are very stable, and their stability is further enhanced by the large gaps of the highest occupied molecular orbital and the lowest unoccupied molecular orbital (HOMO–LUMO gaps). Our findings offer potential applications in building blocks for assembling materials with superatoms.     

Electronic and structural properties of Ti9XO20 (X=Ti,C, si,Ge, Sn and pb) clusters: A DFT study

The electronic and structural properties of Ti₉XO₂₀ (X=Ti, C, Si, Ge, Sn and Pb) clusters have been obtained in the density functional theory (DFT) framework. The changes in the bond length, binding energy, frontier orbitals, and electronic potential have been fully analyzed when one titanium atom in the (TiO₂)₁₀ cluster is replaced by elements with four valence electrons. When one titanium atom is substituted by one carbon atom, a charge excess among the guest and the surrounding oxygen atoms is generated, which is approximately 1.5 times that of the pristine case, and this structure has been shown to be the most stable among the studied systems. In addition, the Ti₁₀O₂₀–Cd₂ and Ti₉CO₂₀–Cd₂ clusters exhibit HOMO–LUMO gaps that have decreased by 0.58 and 2.12 eV, respectively, with respect to the bare cases.     

Geometrical,electronic, and magnetic properties of CunFe (n=1–12) clusters: A density functional study

The geometrical, electronic, and magnetic properties of small Cu_nFe (n=1–12) clusters have been investigated by using density functional method B3LYP and LanL2DZ basis set. The structural search reveals that Fe atoms in low-energy Cu_nFe isomers tend to occupy the position with the maximum coordination number. The ground state Cu_nFe clusters possess planar structure for n=2–5 and three-dimensional (3D) structure for n=6–12. The electronic properties of Cu_nFe clusters are analyzed through the averaged binding energy, the second-order energy difference and HOMO–LUMO energy gap. It is found that the magic numbers of stability are 1, 3, 7 and 9 for the ground state Cu_nFe clusters. The energy gap of Fe-encapsulated cage clusters is smaller than that of other configurations. The Cu₅Fe and Cu₇Fe clusters have a very large energy gap (>2.4 eV). The vertical ionization potential (VIP), electron affinity (EA) and photoelectron spectra are also calculated and simulated theoretically for all the ground-state clusters. The magnetic moment analyses for the ground-state Cu_nFe clusters show that Fe atom can enhance the magnetic moment of the host cluster and carries most of the total magnetic moment.     

Structures and electronic properties of M@Au<Subscript>6</Subscript> (M=Al,Si, P,S, Cl,Ar) clusters: a density functional theory investigation

The geometries and electronic properties of the 3p electrons atoms doped gold cluster: M@Au₆ clusters (M=Al, Si, P, S, Cl, Ar) have been systematically investigated by using relativistic all-electron density functional theory (VPSR) and scalar relativistic effective core potential Stuttgart/Dresden (SDD) basis. Generalized gradient approximation in the Perdue-Burke-Ernzerhof (PBE) functional form is chosen for geometry optimization. A number of new isomers are obtained for neutral M@Au₆ clusters. Both PBE/VPSR and PBE/SDD methods give similar lowest energy structure of each M@Au₆cluster. With the exception of Ar@Au₆, all doped clusters show larger relative binding energies compared with pure Au₇ cluster. It is found that all the ground-state structures of the M@Au₆ clusters prefer the low symmetry structures, which is very different to the 3d transition-metal impurity doped Au₆ clusters. Our results are in excellent agreement with available experiment data.     

Doping golden clusters: MAu19 and M2Au18 (M = Cu and Na)

The structural and electronic properties of MAu⁻₁₉ and M₂Au⁻₁₈ (M = Cu and Na) have been studied by the relativistic density-functional calculations. It is found that the most stable configurations of CuAu⁻₁₉ and Cu₂Au⁻₁₈ are the face-centered and two-face-centered doped structures based upon the tetrahedral structure Au⁻₂₀. In contrast, the ground states of Na-doped gold clusters (NaAu⁻₁₉ and Na₂Au⁻₁₈) exhibit flat-cage configurations. The PES of these ground states are depicted that may be helpful to identify their configurations in the future experiments. The face-centered and two-face-centered doped tetrahedral structures of CuAu⁻₁₉ and Cu₂Au⁻₁₈ have a large HOMO–LUMO gap, indicating that they are chemically stable.     

Ab initio calculation of the electronic and vibrational properties of metal‐organic molecules based on cyclic C6 intercalated with some group VIII transition metals

The vibrational and electronic properties of a new class of organometallic sandwich molecules, (C₆)_nMe_n‐1, based on stacks of cyclic C₆ intercalated with Fe and Ru have been studied using first principles density functional techniques (DFT). Spectral properties as well as the HOMO‐LUMO gap energy in molecules containing up to eight C₆ layers have been calculated. The HOMO‐LUMO energy gap in these molecules is < 1 eV and decreases significantly in longer molecules. It is shown that infinite chains should have excellent metallic properties. These molecules are promising for nanoelectronic applications, due to their predicted high stability, conductivity, and magnetic properties.     

Spin-polarised DFT study of cobalt-doped gallium clusters

The structural, electronic and magnetic properties of small gallium clusters doped with Cobalt have been studied using spin-polarised density functional theory. The binding energy per atom, second-order differences of total energies and fragmentation energies of equilibrium geometries of the host Ga_n+1 and doped Ga_nCo (n = 1–12) clusters are computed. Doped clusters are found to be more stable than pure Ga clusters; Ga₃Co, Ga₅Co and Ga₈Co clusters are exceptionally stable. Doping with Co changes the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO–LUMO) gap, and also affects the magnetic moments of clusters.     

B12N12纳米笼：潜在的二氧化氮检测传感器

利用密度泛函理论通过计算吸附能量、HOMO/LUMO能隙变化、电荷转移、结构扭曲等研究二氧化氮分子在B12N12纳米笼的吸附．此外,通过计算B₁₂N₁₂的电子结合能、Gibbs自由能、态密度和分子表面的静电势研究其稳定性和其它特性．B₁₂N₁₂纳米笼吸附二氧化氮显示三种构型．B₁₂N₁₂团簇的HOMO/LUMO能隙变化对二氧化氮分子的存在非常敏感,从自由团簇的6.84 eV降为NO₂/团簇稳定团簇的3.23 eV．团簇的导电性被极大地提高,表明B₁₂N₁₂纳米簇可能是潜在的二氧化氮气体分子检测传感器.