Evolution of the atomic and electronic structures of CuO clusters: a comprehensive study using the DFT approach.

One of the most fundamental aspects of cluster science is to understand the structural evolution at the atomic scale. In this connection, here we report a comprehensive study of the atomic and electronic structures of (CuO)n clusters for n = 1 to 12 using DFT-based formalisms. Both the plane wave-based pseudo-potential approach and LCAO-MO-based method have been employed to obtain the ground state geometries of neutral, cation and anion copper oxide clusters. The results reveal that neutral copper oxide clusters favor a planar ring structure up to heptamer and from octamer onwards they adopt a three-dimensional motif with (CuO)9 and (CuO)12 forming a barrel-shaped layered structure. Detailed electronic structure analysis reveals that the transition of the atomic structure from 2D to 3D is guided by the energy balance of the Cu-O (d-p) and Cu-Cu (d-d) bonds. The removal of one electron from the cluster (cation) results in slightly stretched bonds while the addition of one electron (anion) showed compression in the overall geometries. The thermodynamic and electronic stability of these clusters has been analyzed by estimating their binding energy, ionization energy and electron affinity as a function of size. Remarkably, among these clusters, the octamer (CuO)8 and dodecamer (CuO)12 show higher binding energy and electron affinity (∼6.5 eV) with lower ionization energy (5.5-6.0 eV). This unique feature of the octamer and dodecamer indicates that they are very promising candidates for both oxidizing and reducing agents in different important chemical reactions.

Composition-dependent photoluminescence in nanocrystalline La2Hf2-xZrxO7:Eu phosphor: role of chemical twin Zr/Hf environments around a luminescent center.

Based on chemical intuition, linear trends are anticipated in Eu3+ photoluminescence performance inside a pyrochlore matrix of the chemical twins, Hf and Zr, owing to probable geometrical and chemical similarity around the luminescent center. The present work reports the drastically fluctuating result of doping Eu3+ in nanocrystalline pyrochlore, La2Hf2-xZrxO7 (LHZO), matrix on composition variation; the variation is counter to the anticipation-based chemical brotherhood of Hf and Zr. Zirconium-enriched samples of LHZO improve asymmetry around Eu3+ ion leading to enhanced photoluminescence quantum yield (PLQY). The samples with compositions 0.7Hf and 1.3Zr depict the lowest non-radiative channels with the highest theoretically calculated PLQY of ∼71% and excellent thermal stability (∼91%). Synergistic experimental and theoretical analysis reveals that Eu does not unbiasedly occupy La-sites in the pyrochlore LHZO matrix towards chemical twins of Hf and Zr; rather, it energetically prefers to occupy Zr-rich vicinal sites. When the composition with Zr is in the low-medium range, Eu has a higher probability of occupying Zr-rich vicinal sites depicting higher lifetime and PLQY. When Zr-content goes beyond 70-80%, the other site occupancies start contributing leading to a reduction in both lifetime and quantum yield. This work paves a great strategy and provides a futuristic potential to utilize europium luminescence in separating chemically close Hf-Zr for various technological applications.

Controlled synthesis of photoresponsive bismuthinite (Bi2S3) nanostructures mediated through a new 1D bismuth-pyrimidylthiolate coordination polymer as a molecular precursor.

Bismuthinite (Bi2S3) nanostructures have garnered significant interest due to their appealing photoresponsivity which has positioned them as an attractive choice for energy conversion applications. However, to utilize their full potential, a simple and economically viable method of preparation is highly desirable. Herein, we present the synthesis and characterization including structural elucidation of a new air- and moisture-stable bismuth-pyrimidylthiolate complex. This complex serves as an efficient single-source molecular precursor for the facile preparation of phase-pure Bi2S3 nanostructures. Powder X-ray diffraction (PXRD), Raman spectroscopy, electron dispersive spectroscopy (EDS) and electron microscopy techniques were used to assess the crystal structure, phase purity, elemental composition and morphology of the as-prepared nanostructures. This study also revealed the profound effects of temperature and growth duration on the crystallinity, phase formation and morphology of nanostructures. The optical band gap of the nanostructures was tuned within the range of 1.9-2.3 eV, which is blue shifted with respect to the bulk bandgap and suitable for photovoltaic applications. Liquid junction photo-electrochemical cells fabricated from the as-prepared Bi2S3 nanostructure exhibit efficient photoresponsivity and good photo-stability, which project them as promising candidates for alternative low-cost photon absorber materials.

Molecular precursor-mediated facile synthesis of phase pure metal-rich digenite (Cu1.8S) nanocrystals: an efficient anode for lithium-ion batteries.

Copper sulfides have gained significant attention as alternative electrodes for rechargeable batteries. A simple and easily scalable synthetic pathway to access these materials is highly desirable. This paper describes the facile synthesis of metal-rich digenite Cu1.8S nanocrystals from a structurally characterized new single-source molecular precursor in various high boiling solvents of varied polarity. The as-prepared nanostructures were thoroughly characterized by PXRD, Raman spectroscopy, EDS, XPS, electron microscopy techniques and diffuse reflectance spectroscopy to understand the crystal structure, phase purity, elemental composition, morphology and band gap. It was found that the reaction solvent has a profound role on their crystallite size, morphology and band gap, however the crystal structure and phase purity remained unaffected. Pristine Cu1.8S nanostructures have been employed as an anode material in lithium-ion batteries (LIBs). The cell delivers a high initial charge capacity of ∼462 mA h g-1 and retains a capacity of 240 mA h g-1 even after 300 cycles at 0.1 A g-1. DFT calculations revealed that multi-size polyhedron layers in the direction perpendicular to the two Li movement channels aid in the sustainable uptake of Li atoms with controlled volume expansion. The structure-mediated flexibility of the metal-rich Cu1.8S lattice during lithiation permits high cyclability with reasonable retention of capacity.

Facile one pot synthesis of highly photoresponsive coinage metal selenides (Cu1.8Se and Ag2Se) achieved through novel Cu and Ag pyridylselenolates as molecular precursors.

Copper selenide (Cu1.8Se) and silver selenide (Ag2Se) have garnered unprecedented attention as efficient absorber materials for cost-effective and sustainable solar cells. Phase pure preparation of these exotic materials in a nano-regime is highly desirable. This account outlines a simple and easily scalable pathway to Cu1.8Se and Ag2Se nanocrystals using novel complexes [Cu{2-SeC5H2(Me-4,6)2N}]4 (1), [Ag{2-SeC5H2(Me-4,6)2N}]6 (2) and [Ag{2-SeC5H3(Me-5)N}]6·2C6H5CH3 (3·2C6H5CH3) as single source molecular precursors (SSPs). Structural studies revealed that the Cu and Ag complexes crystallize into tetrameric and hexameric forms, respectively. This observed structural diversity in the complexes has been rationalized via DFT calculations and attributed to metal-metal bond endorsed energetics. The thermolysis at relatively lower temperature in oleylamine of complex 1 afforded cubic berzelianite Cu1.8Se and complexes 2 and 3 produced orthorhombic naumannite Ag2Se nanocrystals. The low temperature synthesis of these nanocrystals seems to be driven by the observed preformed Cu4Se4 and Ag6Se6 core in the complexes which have close resemblance with the bulk structure of the final materials (Cu1.8Se and Ag2Se). The crystal structure, phase purity, morphology, elemental composition and band gap of these nanocrystals were determined from pXRD, electron microscopy (SEM and TEM), EDS and DRS-UV, respectively. The band gap of these nanocrystals lies in the range suitable for solar cell applications. Finally, these nanocrystal-based prototype photo-electrochemical cells exhibit high photoresponsivity and stability under alternating light and dark conditions.

Multifunctional Lanthanide-Doped Binary Fluorides and Graphene Oxide Nanocomposites Via a Task-Specific Ionic Liquid.

Graphene oxide-based nanocomposites (NCMs) exhibit diverse photonic and biophotonic applications. Innovative nanoengineering using a task-specific ionic liquid (IL), namely, 1-butyl-3-methyl tetrafluoroborate [C4mim][BF4], allows one to access a unique class of luminescent nanocomposites formed between lanthanide-doped binary fluorides and graphene oxide (GO). Here the IL is used as a solvent, templating agent, and as a reaction partner for the nanocomposite synthesis, that is, "all three in one". Our study shows that GO controls the size of the NCMs; however, it can tune the luminescence properties too. For example, the excitation spectrum of Ce3+ is higher-energy shifted when GO is attached. In addition, magnetic properties of GdF3:Tb3+ nanoparticles (NPs) and GdF3:Tb3+-GO NCMs are also studied at room temperature (300 K) and very low temperature (2 K). High magnetization results for the NPs (e.g., 6.676 emu g-1 at 300 K and 184.449 emu g-1 at 2 K in the applied magnetic field from +50 to -50 kOe) and NCMs promises their uses in many photonic and biphotonic applications including magnetic resonance imaging, etc.

Molecular Level Dissection of Critical Spike Mutations in SARS-CoV-2 Variants of Concern (VOCs): A Simplified Review.

SARS-CoV-2 virus during its spread in the last one and half year has picked up critical changes in its genetic code i.e. mutations, which have leads to deleterious epidemiological characteristics. Due to critical role of spike protein in cell entry and pathogenesis, mutations in spike regions have been reported to enhance transmissibility, disease severity, possible escape from vaccine-induced immune response and reduced diagnostic sensitivity/specificity. Considering the structure-function impact of mutations, understanding the molecular details of these key mutations of newly emerged variants/lineages is of urgent concern. In this review, we have explored the literature on key spike mutations harbored by alpha, beta, gamma and delta 'variants of concern' (VOCs) and discussed their molecular consequences in the context of resultant virus biology. Commonly all these VOCs i.e. B.1.1.7, B.1.351, P.1 and B.1.617.2 lineages have decisive mutation in Receptor Binding Motif (RBM) region and/or region around Furin cleavage site (FCS) of spike protein. In general, mutation induced disruption of intra-molecular interaction enhances molecular flexibility leading to exposure of spike protein surface in these lineages to make it accessible for inter-molecular interaction with hACE2. A disruption of spike antigen-antibody inter-molecular interactions in epitope region due to the chemical nature of substituting amino acid hampers the neutralization efficacy. Simplified surveillance of mutation induced changes and their consequences at molecular level can contribute in rationalizing mutation's impact on virus biology. It is believed that molecular level dissection of these key spike mutation will assist the future investigations for a more resilient outcome against severity of COVID-19.

Why Do Relative Intensities of Charge Transfer and Intra-4f Transitions of Eu3+ Ion Invert in Yttrium Germanate Hosts? Unravelling the Underlying Intricacies from Experimental and Theoretical Investigations.

The dominant intensity of parity-forbidden intra-4f transitions of europium(III) over O → Eu charge-transfer band (CTB) intensity is against common perceptions, yet this trend is observed in many germanate hosts and has not been rationalized so far. In search of a plausible explanation for this unusual trend, present work reports an experimental and theoretical investigations in conjunction on two sibling germanate host, namely, Y2GeO5 and Y2Ge2O7 having dopant Eu3+ in their respective YO7 polyhedra. Whereas for Y2GeO5:Eu3+, the CTB is more intense than the intra-4f transitions in the excitation spectrum, in the case of Y2Ge2O7:Eu3+, the relative intensities of CTB and intra-4f transitions are reversed. Comparative structural analysis reveals that Eu3+ present in YO7 of Y2GeO5 has a greater number of tetra-coordinated oxygen (Otetra) and yttrium atom as first and second neighbors, respectively (Eu3+-Otetra-Y3+ linkages). Conversely, in Y2Ge2O7 host, the Eu3+ ion mostly has tricoordinated oxygen (Otri) as its nearest neighbor and germanium ions next to Otri (Eu3+-Otri-Ge4+ linkage). Theoretical calculations reveal that while Y2GeO5:Eu has Otetra(4Y) dominating at the Fermi level and the 4f state of Eu3+ remains inert toward mixing, in Y2Ge2O7:Eu, the Fermi level has major contribution from Otri(2Y + 1Ge) with significant mixing with 4f states of Eu. The dominant control of Eu3+-Otri-Ge4+ linkages in geometrical and electronic structure of Y2Ge2O7:Eu owing to the GeO4 surrounding has been attributed to relative poor intensity of O → Eu CTB. Siege of Eu3+ by GeO4 and subsequent occurrence of Eu3+-Otri-Ge4+ linkages play a dual role: First, it induces electronic rigidity to hinder excitation of electron at bridging (Otri) oxygen by highly charged small Ge4+ cation; second, the covalent character in Eu-O bond is achieved by intermixing of Eu's 4f and Otri 2p orbital which facilitates relaxing of the parity-selection rule thus enhancing the probability of intra-4f transitions. The inferences drawn remain valid when extrapolated to other inorganic oxides having EuOx polyhedra surrounded by covalent units like PO4, SiO4, etc. and have a prevailing number of low-coordinated oxygen atoms and highly charged small cation in the first and second coordination shells, respectively. The optical basicity concept is also found to endorse our explanation. These remarkable generic inferences will pave the rational way for designing efficient phosphors for solid-state lighting.

Single atom alloy catalyst for SO3 decomposition: enhancement of platinum catalyst's performance by Ag atom embedding.

Recently, single atom alloy catalysts (SAA) have shown improved catalytic activity in numerous catalytic reactions. However, to date, single atom alloy (SAA) catalyst is not available for SO3 decomposition reaction, which is a key reactions in the hydrogen economy. Using state of the art density functional theory, we report a novel single Ag atom alloy Pt catalyst in the sub-nanometer length scale (AgPt9@Al2O3) showing superior catalytic behavior for SO3 decomposition. It was found that alloying the alumina-supported platinum nanocluster with a single Ag atom lowers the activation barrier for S-O bond breaking by more than 50% in comparison with the pristine platinum counterpart. Activation barrier for AgPt9@Al2O3 catalyst is 0.52 eV, which is the lowest of any platinum based catalyst reported so far. At variance with pure Pt10@Al2O3, which tries to detach from the support during decomposition reaction, single atom alloy (SAA) nanocluster AgPt9@Al2O3 enhances binding with support, thus strengthening sintering resistance. Notably, influence of single Ag atom is also observed at larger length scale, i.e., at Pt(111) slab, where single Ag atom substituted surface Ag1Pt(111) shows ∼30% reduction in activation barrier in contrast to a pristine surface. Single Ag atom works in bifunctional mode as it not only reduces the activation barrier, but also simultaneously weakly adsorbs the reaction product SO2, signifying relatively easier desorption and better recyclability. Deeper location of silver d-electrons and lesser electronegativity of silver is responsible for the better performance of single Ag atom alloyed Pt catalyst. We strongly believe that these remarkable results will open new avenues for future designing and fabrication of cost-effective catalysts for SO3 decomposition.

Bimetallic Ag-Pt Sub-nanometer Supported Clusters as Highly Efficient and Robust Oxidation Catalysts.

A combined experimental and theoretical investigation of Ag-Pt sub-nanometer clusters as heterogeneous catalysts in the CO→CO2 reaction (COox) is presented. Ag9 Pt2 and Ag9 Pt3 clusters are size-selected in the gas phase, deposited on an ultrathin amorphous alumina support, and tested as catalysts experimentally under realistic conditions and by first-principles simulations at realistic coverage. In situ GISAXS/TPRx demonstrates that the clusters do not sinter or deactivate even after prolonged exposure to reactants at high temperature, and present comparable, extremely high COox catalytic efficiency. Such high activity and stability are ascribed to a synergic role of Ag and Pt in ultranano-aggregates, in which Pt anchors the clusters to the support and binds and activates two CO molecules, while Ag binds and activates O2 , and Ag/Pt surface proximity disfavors poisoning by CO or oxidized species.

ORR viability of alumina-supported platinum nanocluster: exploring oxidation behaviour by DFT.

While alumina-supported platinum particles are versatile for several oxidation reactions, their viability as ORR catalysts has not been explored to date. Therefore, to assess the prospects of alumina-supported platinum nanoclusters in ORRs, a systematic DFT study has been carried out to explore the oxidation behavior of a Ptn@Al2O3 (n = 1-7, 10) cluster. The results are compared with the oxidation behavior of the corresponding gas phase platinum cluster and that of an extended Pt(111) slab. Both supported and unsupported clusters activate adsorbed oxygen molecules and energetically favor dissociative chemisorption of oxygen, leading to stable oxide formation with Pt-O-Pt linkages. However, the influence of the alumina substrate downshifts the d-band centre of the platinum cluster, which not only reduces the reaction enthalpy of oxidation by 8-10%, but also elongates the Pt-O bond of the oxide product by 3-8%. These observations indicate that removal of oxide will be relatively easier for supported clusters than for unsupported clusters. Cluster binding is found to sustain during oxidation, as oxidation of the platinum host cluster results in reduction of the distance between the cluster and support surface. While the gas phase Pt10 cluster does not show any similarity to the oxidation behavior shown by THE Pt(111) slab, the Pt10@Al2O3 cluster reveals close resemblance. Both the Pt(111) slab and Pt10@Al2O3 cluster form similar oxide products, having tri-coordinated oxygen with comparable Pt-O bond distances. The observed resemblance has been attributed to the similarity in the electronic structure and d-band centre position of the platinum surface and alumina-supported Pt10 cluster. Whilst this similar oxidation behaviour of the Pt10@Al2O3 cluster endorses its viability as an ORR catalyst, further modulation of this catalyst is desirable to improve its potential.

Platinum-Mediated Activation of Coordinated Organonitriles by Telluroethers in Tetrahydrofuran: Isolation, Structural Characterization, and Density Functional Theory Analysis of Intermediate Complexes.

The reactions of [PtCl2(NCR)2] with telluroethers (ArAr'Te) in organic solvents have been investigated. The reactions in dichloromethane yield [PtCl2(TeArAr')2], while those in tetrahydrofuran (THF) give different products depending on the steric demands of the aryl groups on tellurium, the molarity of the reactants, and the reaction conditions. The reactions between [PtCl2(PhCN)2] and TeArAr' in 1:1 molar ratio at room temperature in THF yield several products, like [PtCl2(TeArAr')2] (Ar/Ar' = Ph/Ph, o-tol/Mes, Mes/Mes), [PtCl2(PhCN){NC(O)Ph[TeMes(o-tol)]}], and [PtCl2{NC(O)Ph(TeMes2)}2]. The reaction with TeMes2 in refluxing THF gave [PtCl2{NC(Ph)C4H7O}{NC(O)Ph(TeMes2)}] and [PtCl(TeMes2){Te(Mes)CH2C6H2Me2}], depending on the duration of heating. Reaction of [PtCl2(PhCN)2] with TeArMes afforded [PtCl2(TeArMes)2] (Ar = Ph, o-tol, and Mes), the formation of which decreased with increasing steric demand of the Ar group, together with [PtCl2{NC(O)Ph(TeArMes)}2]. The telluroether in the latter binds to nitrogen, and tellurium exists in the formal oxidation state of +4 (from XPS). The tellurium in these complexes exhibits secondary interactions with platinum (J((195)Pt-(125)Te) = 309-347 Hz) and with the carbonyl oxygen. These complexes slowly dissociate in solution to give [PtCl2(TeMesAr){NC(O)Ph(TeMesAr)}], finally leading to the formation of [PtCl2(TeMesAr)2]. Molecular structures of trans-[PtCl2(PhCN){NC(O)Ph[TeMes(o-tol)]}], trans-[PtCl2{NC(O)Ph(TeMes2)}2], trans-[PtCl2{NC(Ph)C4H7O}{NC(O)Ph(TeMes2)}], trans-[PtCl2{NC(O)Ph[TeMes(o-tol)]}2], trans-[PtCl2(TeMes2){NC(O)Ph(TeMes2)}], trans-[PtCl2{NC(O)Me(TeMes2)}2], and [PtCl(Te-o-tol){NC(O)Ph}2] have been unambiguously established by single-crystal X-ray diffraction analyses. Density functional theory calculations for some of the complexes were performed, and geometrical parameters are in good agreement with the values obtained from X-ray analyses.

Speciation and site occupancy of uranium in strontium orthosilicate by photoluminescence and X-ray absorption spectroscopy: A combined experimental and theoretical approach.

Identifying the oxidation state and coordination geometry of radioactive element like uranium is important to fully understand its toxicology and other harmful effect in environment. Strontium orthosilicate is taken as a model compound for that. Strontium silicate doped with 1.0 mol% of U has been synthesized using sol-gel method and characterized using X-ray diffraction (XRD), time resolved fluorescence spectroscopy (TRFS) and extended X-ray absorption fine structure (EXAFS). Uranium exhibits multiple oxidation state and each one of them is having characteristics luminescence is an interesting dopant from structural point of view. TRFS is used to investigate the oxidation state and coordination behavior of uranium in Sr2SiO4. From TRFS measurement it was observed that uranium stabilizes in +6 oxidation state in the form of uranyl ion. Based on luminescence lifetime and EXAFS studies it was inferred that uranyl is stabilized on both 9- and 10-coordinated strontium polyhedra but majority occupies relatively asymmetric 9-coordinated Sr sites. This is further confirmed using theoretical measurement.

Modulation of band gap by an applied electric field in silicene-based hetero-bilayers.

Electronic properties of the hetero-structures consisting of silicene, graphene and BN monolayers under the influence of an electric field were investigated using density functional theory. With no electric field, both silicene/graphene and silicene/BN were shown to have a finite gap of about ∼50 meV, though silicene is a zero-gap two-dimensional material. Application of the field perpendicular to the bilayer system was found to facilitate modulation of the band gap, exhibiting an approximately linear relationship with the gap energy, in contrast to what was seen for the constituent monolayers. Also, the degree of the modulation was mainly determined by the Si-pz electronic states at the interface of the silicene/graphene and silicene/BN bilayers.

Evidence of a graphene-like Sn-sheet on a Au(111) substrate: electronic structure and transport properties from first principles calculations.

Two dimensional nanostructures of group IV elements have attracted a great deal of attention because of their fundamental and technological applications. A graphene-like single layer of tin atoms, commonly called stanene, has recently been predicted to behave like a quantum spin Hall insulator. Here we report the atomic structure, stability and electron transport properties of stanene stabilized on a gold substrate. The optimization of geometry and electronic structure was carried out using a plane-wave based pseudo-potential approach. This work is divided into three parts: (i) the nature of chemical interaction between tin atoms and the gold support, (ii) the geometrical shape and electronic structure of the tin layer on the gold support and (iii) the electron transport behavior of the gold supported tin layer. The results show that tin atoms bind to the gold support through strong chemical bonds and significant electronic charge transfer occurs from tin to the gold support. Remarkably, for a layer of tin atoms, while a buckled structure is preferred in the free state, a planar graphene-like atomic arrangement is stabilized on the gold support. This structural change corroborates the metal-like band structure of the planar stanene in comparison to the semi-metallic buckled configuration. The tunneling current of the supported tin layer shows Ohmic-like behavior and the calculated STM pattern of the supported tin layer shows distinct images of 'holes', characteristic of the hexagonal lattice.

The structural and electronic properties of Au(n) clusters on the α-Al2O3(0001) surface: a first principles study.

We report the structural and electronic properties of Aun (n = 1-7 and 10) clusters supported on a clean α-Al2O3(0001) surface using the spin-polarized version of the plane wave based pseudo-potential method. To underscore the effect of support interaction, the geometries of the deposited Au clusters are compared with the gas-phase structures. In general, the trend in the growth pattern shows that all deposited Au clusters favor planar configurations, similar to that in the isolated case. However, due to the roughness of the Al2O3(0001) surface the deposited Au atoms are arranged in a zig-zag pattern. The binding energy of an Au atom on the Al2O3 surface is 0.79 eV and it binds to the surface Al atom. Two Au atoms prefer to form a dimer on the alumina surface rather than adsorbing as a monomer at a long distance. As the size of the cluster increases the adsorption energy shows a decreasing trend. The nature of chemical bonding at the interface is established by the charge distribution analysis, which suggests an overall charge transfer from the surface to the Au cluster. The additional negative charge on the deposited Au cluster corroborates the red shift of the energy levels of the Au-Al2O3 composite in comparison to the isolated Aun clusters. Further investigations were carried out by analyzing the interaction between the oxygen molecule and the Aun@Al2O3 system, a prototype to study the oxidation mechanism. The results reveal that the interaction of O2 with Aun@Al2O3 follows a dissociative chemisorption route and ruptures the O-O bond.

Growth pattern of Ag(n) (n = 1-8) clusters on the α-Al2O3(0001) surface: a first principles study.

We report an extensive first-principles study of the structure and electronic properties of Ag(n) (n = 1-8) clusters isolated in gas phase and deposited on the α-Al(2)O(3) surface. We have used the plane wave based pseudopotential method within the framework of density functional theory. The electron ion interaction has been described using projector augmented wave (PAW), and the spin-polarized GGA scheme was used for the exchange correlation energy. The results reveal that, albeit interacting with support alumina, the Ag atoms prefers to remain bonded together suggesting an island growth motif is preferred over wetting the surface. When compared the equilibrium structures of Ag clusters between free and on alumina substrate, a significant difference was observed starting from n = 7 onward. While Ag(7) forms a three-dimensional (3D) pentagonal bipyramid in the isolated gas phase, on alumina support it forms a planar hexagonal structure parallel to the surface plane. Moreover, the spin moment of the Ag(7) cluster was found to be fully quenched. This has been attributed to higher delocalization of electron density as the size of the cluster increases. Furthermore, a comparison of chemical bonding analysis through electronic density of state (EDOS) shows that the EDOS of the deposited Ag(n) cluster is significantly broader, which has been ascribed to the enhanced spd hybridization. On the basis of the energetics, it is found that the adsorption energy of Ag clusters on the α-Al(2)O(3) surface decreases with cluster size.

Novel properties of boron nitride nanotubes encapsulated with Fe, Co, and Ni nanoclusters.

Using state of the art spin polarized density functional theory, we report the stability and structural aspects of small magnetic clusters M(4) (M = Fe, Co, and Ni) inside an inert boron nitride nanotube [BNNT(10,0)]. The geometry optimization was carried out starting with various possible configurations [one-dimensional (1D) linear chain, two-dimensional (2D) planar rhombus, and three-dimensional (3D) tetrahedral], and the results reveal that the ground state geometry of M(4) cluster inside the nanotube favors 3D configuration over others. Moreover, these small clusters are found to retain their magnetic nature with a small reduction in the total magnetic moment even after encapsulation. The radial confinement effect on the atomic structure of M(4) clusters was investigated by optimizing the Co(4) (prototype example) in BNNT(10, 0), BNNT(9, 0), and BNNT(8, 0). It is found that with the increase in radial confinement (smaller diameter), the Co(4) cluster becomes more compact, which further leads to significant changes in the electronic and magnetic properties. The electronic density of states analysis of the M(4) clusters inside BNNT(10,0) showed the appearance of additional electronic states in the band gap of BNNT(10, 0). In order to underscore the possibility of functionalizing these encapsulated tubes, we have performed the adsorption of oxygen molecules on it. The adsorption of oxygen in the molecular form with elongated O-O bonds further justifies its application in the oxidative catalysis.

M atom (M = Cu, Ag and Au) interaction with Ag and Au substrates: a first-principles study using cluster and slab models.

Using state-of-the-art first-principles calculations we report the interaction of M atoms (M = Cu, Ag and Au) with small Ag(n), Au(n) clusters (n = 3 and 6) and periodic Ag(111) and Au(111) surfaces. All calculations were performed using the plane wave pseudo-potential approach under the spin polarized version of the generalized gradient approximation scheme. The result shows that the equilibrium geometry of all MAg(3) and MAu(3) clusters favor a planar rhombus structure. From the charge distribution analysis of MAg(n)/MAu(n) clusters it is found that, while Cu and Ag donates electronic charge towards the host clusters, the Au atom acts as an acceptor, thus creating charge polarization in the system. The difference in orbital decomposed charges before and after the M interaction reveals that enhanced s-d hybridization is responsible for keeping the MAu(6) cluster planar, and increased p-orbital participation induces three-dimensional configurations in MAg(6) clusters. The optimization of M atom deposition on the Ag(111) and Au(111) surfaces shows that M atoms prefer to adsorb on the threefold fcc site over other well-defined sites. From the orbital decomposed charge analysis it is inferred that, although there is significant difference in the absolute magnitude of the interaction energy between M atoms and the Ag or Au substrates, the nature of chemical bonding is similar for the finite size clusters as well as in slab models.

Growth pattern and electronic properties of acetonitrile clusters: a density functional study.

We report a systematic theoretical study on the growth pattern and electronic properties of acetonitrile clusters [(CH(3)CN)(n) (n = 1, 9, 12)] using density functional approach at the B3LYP6-31++G(d,p) level. Although we have considered a large number of configurations for each cluster, the stability of the lowest energy isomer was verified from the Hessian calculation. It is found that the lowest energy isomer of the dimer adopts an antiparallel configuration. For trimer and tetramer, cyclic ring structures were found to be favored over the dipole stabilized structure. In general, it is found that the intermolecular CH...N interactions play a significant role in the stabilization of the cyclic layered geometry of acetonitrile clusters. A critical comparison between trimer and tetramer clusters suggests that the three member cyclic ring is more stable than four member rings. The growth motif for larger clusters (n = 5-9, 12) follows a layered pattern consisting of three or four membered rings, which, in fact, is used as the building block. Based on the stability analysis, it is found that clusters with an even number of molecular entities are more stable than the odd clusters, except trimer and nonamer. The exceptional stability of these two clusters is attributed to the formation of trimembered cyclic rings, which have been found to form the building blocks for larger clusters.