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An analytic expression for the total energy of 4He clusters composed of N atoms is obtained by means of a variational solution of the energy density functional. The energy is calculated as an expansion in decreasing powers of the cluster radius, R∝N1/3. Contributions of volume (R3), surface (R2), curvature (R), constant (R0), (1/R), and (1/R2) are clearly separated in the formula. Chemical potentials, fusion and fission potentials, surface thickness, and unit radii are also obtained. [ABSTRACT FROM AUTHOR]

Recent experiments have shown that Ta@Si16+ is a very stable cation from which it should be possible to create Si-based cluster assembled materials. In this paper we have studied, by means of first-principles spin-dependent generalized gradient approximation calculations, the structural and electronic properties of the following systems: (i) Ta@Sin+ clusters in the range n=14-18; (ii) (Ta@Si16F)m aggregates with sizes m=1-8 formed by Ta@Si16F molecules; (iii) infinite wires formed by stacking triangular (Ta@Si16F)3 aggregates twisted 60° to each other along the vertical axis; and (iv) the fcc phase of bulk Ta@Si16F. The minimum-energy Ta@Si16+ cluster shows C3v symmetry, having 40 meV smaller total energy than a fullerenelike D4d isomer. However, the molecule Ta@Si16F formed with that D4d isomer is 40 meV more stable than that formed with the C3v one. We have optimized several [Ta@Si16F]n aggregates (n=1-8) which contain the Ta@Si16 unit with D4d symmetry. The more bound (Ta@Si16F)6 aggregate is formed by stacking vertically two triangular (Ta@Si16F)3 aggregates which are twisted 60° to each other. The infinite wire formed with that (Ta@Si16F)6 aggregate as the unit cell has a cohesive energy 1.88 eV and a small highest occupied molecular orbital-lowest occupied molecular orbital gap. We have optimized also a metastable fcc bulk phase having the Ta@Si16F supermolecule as the unit cell. A Birch-Murnaghan fit to that phase produces a cohesive energy 0.84 eV at lattice constant 12.27 Å, with bulk modulus 7.55 GPa and a phase stability to isotropic compression smaller than 0.75 GPa. That phase is nonmagnetic and shows a band gap of 0.20 eV. Using the values of hardness of Ta@Si16F molecules, we estimated a correction enhancement factor ~3 to that small band gap. For that metastable solid we performed a 13.5-ps run of first-principles molecular dynamics annealing at 300 K and constant volume, and we found that the Ta@Si16F supermolecule in the fcc cell becomes severely distorted after the first 5 ps. [ABSTRACT FROM AUTHOR]

We present a first-principles pseudopotential optimization of the lower energy equilibrium structure of SinSc- anions for n=14-18. We find that Si16Sc- is more stable than its neighbors clusters, in agreement with recent experimental mass spectra. We also optimize the geometry of pure Sin neutral clusters in the range n=14-18, and compare our results with those from previous first-principles calculations. [ABSTRACT FROM AUTHOR]

The combination of Langevin molecular dynamics for simulated annealing with realistic quantum-mechanical interactions obtained from first principles supercell calculations within the pseudo potential plane-wave method are applied to examine the structural and electronic properties of the following systems i) pure and mixed GenTem (n, m = 0 - 2), Ge3, Te3 and Ge3Te3 semiconductor clusters, and ii) bimetallic PbNan (n ≤ 7) clusters. Results using the local density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange correlation functional are compared with available experimental data. It is found that the GGA leads to larger bond lengths and smaller binding energies than the LDA, but both approximations lead to the same group symmetry for the ground state of these clusters. Two isomeric configurations for PbNa6, having C3v and Oh symmetries, respectively, are found. The dipole moments of semiconductor clusters are compared with those estimated from recent experiments at room temperature. The dipole moments from GGA calculations are, on average, in better agreement with experiments than those calculated with the LDA. [ABSTRACT FROM AUTHOR]

The exchange-correlation potential with the correct −1/r asymptotic behavior proposed by Parr and Ghosh (Phys Rev A 1995, 51, 3564) is used here to study the linear response to external fields of (1) neutral and charged sodium clusters, and (2) doped clusters of the type NanPb (n = 4, 6, 16). Our results for the photoabsorption cross section are compared with experiments, when available, and with previous density functional theory calculations using local and nonlocal functionals. The calculated static polarizabilities and plasmon frequencies are in better agreement with experiments than were previous calculations. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 [ABSTRACT FROM AUTHOR]

We present, based on state of the art density functional theoretic calculations, a new putative ground state (GS) for the cluster (TiO2)10, which results more than 1 eV lower in energy than all those previously reported in the literature. The geometric and electronic properties of this new cluster are discussed in detail and in comparison with the rest. We analyze the implications of the new GS in the context of recent experiments of reactivity regarding oxygen exchange with gaseous CO2 in TiO2 nanostructures, and also in connection with a recent interpretation of photoelectron spectroscopic measurements of the band gap of gas phase TiO2- clusters. [ABSTRACT FROM AUTHOR]

A preface to the periodical "European Physical Journal D--Atoms, Molecules, Clusters & Optical Physics," is presented.

Starting with the nearly spherical endohedral M@Si cage-like clusters (M = Sc, Ti, V) in their fullerene-like isomerical form with D symmetry, we study the trends in the formation of [Ti@Si], [Sc@SiK], and [V@SiF] aggregates as their size increase ( n ≤ 9). We identify specially stable linear, planar, and three-dimensional patterns, which can serve to grow low-dimensional infinite systems. The structure and cohesive energy of a few infinite chains of that type are optimized. We also present calculations of fcc, bcc, and single cubic crystal meta stable phases having the Ti@Si superatom as basic unit, as well as cubic NaCl and CsCl bulk structures of Sc@SiK and V@SiF supermolecules. The orientation and isomerization of the superatom or supermolecule in the cubic cell plays an important role. The projected density of states of V@SiF crystal with NaCl structure shows a meta stable ferromagnetic phase due to polarization of d electrons of vanadium. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

We present a study based on first-principles calculations of the adsorption of CO on selected equilibrium configurations of MAunO2 + (M = Ti, Fe; n = 1, 6, 7) complexes resulting from the adsorption of O2 on doped cationic gold clusters MAun +. Empirical rules for the formation of CO2-MAunO+ complexes are outlined. The desorption energy of CO2 is calculated. The adsorption of a second CO molecule on the residual MAunO+ complex leads in some cases to the formation of CO2-MAun +. The desorption of a second CO2 molecule brings back to the initial doped gold cluster MAun +. [ABSTRACT FROM AUTHOR]

We report on first-principles quantum mechanical optimizations of the minimum energy equilibrium structure of neutral, Si_{n}, and anionic, Si_{n}^{-}, pure silicon clusters, as well as the isoelectronic Si_{n}M doped clusters (M =Sc^{-}, Ti, V^{+}) for n=14–18. We have published previously some of these results, but additional analysis is contributed here for the first time, particularly for the pure anionic silicon clusters and doped Si_{n}Ti compounds. The lowest energy isomer of the anionic Si_{n}^{-} cluster shows different geometry than the neutral cluster, except for n=15, 17. The geometries of a few low-lying energy isomers of doped Si_{n}M does not relate to those of pure silicon clusters in the range of sizes considered in this work. For both pure and doped Si clusters, we analyze the trend of several electronic properties with the cluster size, like the binding energy, the addition energy of the impurity M to pure Si clusters, the second difference of total energy, the Homo-Lumo gap, the average Si-Si and Si-M distance, and the electron affinity. For Si_{16}M doped clusters we found the largest binding energy, the highest second difference of energy, and the highest Homo-Lumo gap. These facts are manifestations of the special stability of Si_{16}M clusters found in recent experimental mass spectra, which was rationalized in previous works as a combination of geometrical (near spherical cage-like structure) and electronic effects (l-selection rule of the spherical potential model). Here we present additional arguments, by comparing the partial orbital density of states of the near-spherical Frank-Kasper isomer of Si_{16}Ti, with that of a non-spherical isomer of Si_{16}Sc^{-} anion. We have also computed the adiabatic electron affinity of pure and doped Si clusters. For doped clusters, the computed electron affinities are in very good agreement with available estimations from experimental photoelectrons spectra, but for pure neutral clusters the calculations underestimate by more than 18% the experimental values. [ABSTRACT FROM AUTHOR]

We have performed a systematic study of the electronic and geometrical structure of several compounds containing first-row transition metal by means of first principles spin-density functional calculations based on norm-conserving pseudo-potentials and numerical basis sets of the double ζ plus polarization type. To achieve a realistic description of these compounds, we find that the pseudo-potentials for 3d elements with d-orbital occupation up to 5 electrons must contain at least the semi-core state 3p in the valence shell. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004 [ABSTRACT FROM AUTHOR]

Recently, Ar physisorption was used as a structural probe for the location of the Ti dopant atom in aluminium cluster cations, AlnTi+ [Lang et al., J. Am. Soc. Mass Spectrom. 22, 1508 (2011)]. As an experiment result, the lack of Ar complexes for n > nc determines the cluster size for which the Ti atom is located inside of an Al cage. To elucidate the decisive factors for the formation of endohedrally AlnTi+, experimentalists proposed detailed computational studies as indispensable. In this work, we investigated, using the density functional theory, the structural and electronic properties of singly titanium doped cationic clusters, AlnTi+ (n = 16–21) as well as the adsorption of an Ar atom on them. The first endohedral doped cluster, with Ti encapsulated in a fcc-like cage skeleton, appears at nc = 21, which is the critical number consistent with the exohedral-endohedral transition experimentally observed. At this critical size the non-crystalline icosahedral growth pattern, related to the pure aluminium clusters, with the Ti atom in the surface, changes into a endohedral fcc-like pattern. The map of structural isomers, relative energy differences, second energy differences, and structural parameters were determined and analyzed. Moreover, we show the critical size depends on the net charge of the cluster, being different for the cationic clusters (nc = 21) and their neutral counterparts (nc = 20). For the AlnTi+ · Ar complexes, and for n < 21, the preferred Ar adsorption site is on top of the exohedral Ti atom, with adsorption energy in very good agreement with the experimental value. Instead, for n = 21, the Ar adsorption occurs on the top an Al atom with very low absorption energy. For all sizes the geometry of the AlnTi+ clusters keeps unaltered in the Arcluster complexes. This fact indicates that Ar adsorption does not influence the cluster structure, providing support to the experimental technique used. For nc = 21, the smallest size of endohedral Ti doped cationic clusters, the Ar binding energy decreases drastically, whereas the Ar-cluster distance increases substantially, point to Ar physisorption, as assumed by the experimentalists. Calculated Ar adsorption energies agree well with available experimental binding energies. [ABSTRACT FROM AUTHOR]

A theoretical study of nanoparticles of indium oxide, one of the most relevant transparent conducting materials, is reported. By means of Density Functional Theory in the generalized gradient approximation, we investigated the atomic and electronic structures of the neutral and charged indium oxide clusters InnOm0/± with n = 1-6 and m = 1-8, as well as related properties like adiabatic ionization potentials and electron affinities. Based on total energy differences between the obtained global minimum configurations of parent clusters and possible fragments, we explored the respective fragmentation channels for cationic clusters and compared our results with those recently observed in Photodissociation measurements (Knight et al. in IJMS 304:29, 2011). The overall good agreement between theory and experiment provides compelling evidence of the calculated properties of these systems, whose knowledge is essential to take advantage of the nanoscale in future technological applications of these materials. [ABSTRACT FROM AUTHOR]

Presents a study which calculated the local magnetic moments and magnetic orders for a Fe(Cr) monolayer adsorbed on a stepped Cr(Fe)(107) substrate. Results obtained; Presentation of two magnetic arrangements obtained for Cr/Fe(107); Magnetic moment in units of µg per atom.

Usingthe density functional method with the generalized gradientapproximation for the exchange and correlation, we investigated thegeometrical and electronic properties of free-standing complexes ofConclusters combined with hydrogen-saturatedboron–nitrogen (BN) rings [(BN)3H6]m. The Co atoms tend to form a subclustercapped by BN rings that preserve the Co subcluster against the environmentand with which they weakly interact. Thus, the Co subcluster is capableof sustaining a noticeable magnetic moment. These facts are relevantfor designing grains with localized magnetic moments. We also optimizedthose TMn[(BN)3H6]ncomplexes with n=1–3 and TM = Fe, Ni, Ru, Rh, and Pd, starting with the ground-stategeometry obtained previously for TM = Co, in order to analyze thedependence of the electronic properties with the number of d electronsin the transition-metal atoms. [ABSTRACT FROM AUTHOR]

Using the generalized gradient approximation (GGA) todensity functionaltheory (DFT), we compute the electronic structure and related magneticproperties of free-standing Co12–xCuxclusters (x= 0–12)with structures resulting from the optimization of those of the low-lyingenergy isomers of pure Co12and Cu12in whichCo(Cu) were replaced by Cu(Co) atoms. Structural transitions for thelowest energy homotop are obtained as a function of the concentration,but in all cases, a clear surface segregation of Cu is found in thelow concentration regime x< 5. The binding energydecreases monotonically when xincreases. The dipolemoment changes abruptly from 0.06 D for x= 2 to0.59 D for x= 3 in coincidence with a structuralchange. The electronegativity of the lowest energy homotop exhibitsminimum (maximum) value for x= 11 (x= 9). The x= 5, 9 clusters show local maxima ofthe hardness, of the excess energy, and of the second difference inenergy, clear indicators of specially stable stoichiometries. Themagnetic behavior of Co12–xCuxis a monotonous function of the Co concentration,decreasing by steps of ≥2 μBfor every Coatom that is replaced by Cu, although for certain concentrations,different spin isomers, sometimes accompanied by structural transitions,are found close to the ground state. Ferromagnetic-like order is obtainedas the ground state in all cases, contrary with the trend found inbinary clusters of the same elements by other authors who predictedantiferromagnetic order. We analyze in detail the possible spin excitationsin Co12Cu to demonstrate that local antiferromagnetic couplingscan only exist as metastable spin states. [ABSTRACT FROM AUTHOR]

We performed ab initio density-functional-theory calculations to investigate the adsorption of molecular hydrogen on pristine and Al-doped hydrogen-passivated zigzag graphene nanoribbons (GNRs) using nonlocal van der Waals functionals that have recently been proposed for an accurate description of exchange and correlation effects in weakly bound systems. Our results, which are compared with those obtained using the standard local density and generalized gradient approximations, show that neither pristine GNRs nor substitutional Al-doped GNRs with an Al atom occupying a central, lateral, or subedge site satisfy the binding-energy criterion specified by the U.S. Department of Energy for novel hydrogen-storage materials. However, the criterion is satisfied by a GNR doped with an Al atom at an edge site and also by zigzag GNRs with adsorbed Al at lateral hole sites. [ABSTRACT FROM AUTHOR]

We present a systematic study of the electronic and geometric structure of neutral and charged noble metal clusters Xnv (X = Cu, Ag, Au; n ≤ 13; v = -1,0,+1), obtained from first principles GGA density functional calculations based on norm-conserving pseudopotentials and a numerical atomic basis set. We determined that the maximum number of atoms forming planar structures with charge v = (-1,0,+1) are (12, 11, 7) for gold, (5, 6, 5) for silver, and (5, 6, 4) for copper clusters. These results are compared with previous experimental and theoretical estimates. We argue that the tendency to planarity of gold clusters, which is much larger than in copper and silver, is strongly favored by relativistic effects, which decrease the s-d electron promotion energy and lead to hybridization of the half-filled 6s orbital with the occupied 5dz2 orbital. Trends for the calculated cohesive energy, average bond lengths, hardness (ionization potential minus electron affinity), and fragmentation energy of the Xnv cluster are presented and discussed in comparison with available experiments and other calculations. [ABSTRACT FROM AUTHOR]

The ionic and electronic structure of (Al2O3)n(Ox) clusters with n ≤ 16 and x = 0, 1, 2 is studied by means of first principles density functional calculations, norm-conserving pseudopotentials and a numerical atomic basis set. The equilibrium geometries have been determined by total energy minimization, starting with several initial geometries for each cluster size. The trends obtained for the atomic arrangements (structural isomers, coordination numbers, “disordered” versus ”ordered” structures, etc.) and the electronic properties (binding energies, Homo-Lumo gap and dipole moments) are discussed. For most of the oxidized clusters studied here we find that the Homo-Lumo gap and the magnitude of dipole moment of isomeric species can vary drastically. [ABSTRACT FROM AUTHOR]

The spin polarization of the vanadium(001) surface is studied by means of first-principles generalized gradient approximation (GGA) calculations within the linear combination of atomic orbitals (LCAO) code Siesta and the norm-conserving pseudopotentials of Troullier–Martins. Whereas the conventional valence 4s23d3 pseudopotential, including nonlinear core corrections (NLCC), leads to a high surface polarization for the 7-, 9-, and 15-layer (001) films of V (with and without relaxation), treating explicitly as valence electrons, the semicore 3p6 state we obtain is a considerable reduction of the magnetic moment at the surface, which became nonmagnetic for the relaxed 15-layer film, in agreement with recent all-electron GGA first-principles calculations. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 [ABSTRACT FROM AUTHOR]