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Computational results are reported for the ground and low-lying excited electronic states of Al3- and Al3 and compared with the available spectroscopic data. In agreement with previous assignments, the six photodetachment transitions observed in the vibrationally resolved 488 nm photoelectron spectrum of Al3- are assigned as arising from the ground X 1A1′(1A1) and excited 3B2 states of Al3- and accessing the ground X 2A1′(2A1) and excited 2A2″(2B1), 4A2, and 2B2 states of Al3 (with C2v labels for D3h states in parentheses). Geometries and vibrational frequencies obtained by PBE0 hybrid density functional calculations using the 6-311+G(3d2f) basis set and energies calculated using coupled cluster theory with single and double excitations and a quasiperturbative treatment of connected triple excitations (CCSD(T)) with the aug-cc-pVxZ {x=D, T, Q} basis sets with exponential extrapolation to the complete basis set limit are in good agreement with experiment. Franck–Condon spectra calculated in the harmonic approximation, using either the Sharp–Rosenstock–Chen method which includes Duschinsky rotation or the parallel-mode Hutchisson method, also agree well with the observed spectra. Possible assignments for the higher-energy bands observed in the previously reported UV photoelectron spectra are suggested. Descriptions of the photodetachment transition between the Al3- and Al3 ground states in terms of natural bond order (NBO) analyses and total electron density difference distributions are discussed. A reinterpretation of the vibrational structure in the resonant two-photon ionization spectrum of Al3 is proposed, which supports its original assignment as arising from the X 2A1′ ground state, giving an Al3 bond dissociation energy, D0(Al2–Al), of 2.403±0.001 eV. With this reduction by 0.3 eV from the currently recommended value, the present calculated dissociation energies of Al3, Al3-, and Al3+ are consistent with the experimental data. [ABSTRACT FROM AUTHOR]

By incorporating kinetic-energy density in a balanced way in the exchange and correlational functionals and removing self-correlation effects, we have designed a density functional that is broadly applicable to organometallic, inorganometallic, and nonmetallic bonding, thermochemistry, thermochemical kinetics, and noncovalent interactions as well as satisfying the uniform electron gas limit. The average error is reduced by a factor of 1.3 compared with the best previously available functionals, but even more significantly, we find a functional that has a high accuracy for all four categories of interaction. [ABSTRACT FROM AUTHOR]

The thermodynamic properties of Al are calculated for two nonpairwise-additive potentials by using Monte Carlo simulations. The results have shown that the melting point for the embedded-atom model is higher than the experimental value and the embedded-atom (EAM) potential has yielded improved binding energies for smaller clusters, a small fraction of aggregates in the saturated vapor phase, and hence an accurate heat of vaporization and boiling point.

Electrode poisoning by CO is a major concern in fuel cells and hence the use of relativistic effective core potentials for the treatment of PdCO and for metal-CO interactions, where the predominant bonding mechanism is charge transfer, is justified. The hybrid density functional theory can quantitatively and qualitatively predict the nature of the [sigma]-donation/[pi]-back-donation mechanism that is associated with the Pd-CO and [Pd.sub.2]-CO bonds.

Fourty-two different functionals are tested, comprising 2 local spin density approximation (LSDA) functionals, 12 generalized gradient approximation (GGA) methods, 13 hybrid GGAs, 7 meta GGA methods, and 8 hybrid meta GGAs. GGA density functionals are more accurate for the atomization energies of pure transition metal systems than are their meta, hybrid, or hybrid meta analogues are founded.

A scheme for parametrizing analytic potential energy functions (PEFs) for nanoparticle systems that uses a limited set of bulk data and electronic structure calculations for small clusters was described. The scheme was validated using pure aluminum systems.

Nineteen analytic potential energy functions (PEFs) for aluminium were obtained from the literature. The data set was also used to develop, parameterize and systematically study the effectiveness of several functional forms.

The geometries of and atomization energies of small aluminum clusters (Al2-Al7) are calculated with the highly accurate multicoefficient Gaussian-3 version 3 method (MCG3/3). The Al clusters, with diameters up to 0.7 nm, are studied in order to develop some methods that are suitable to predict the properties of nanoparticles.

The coefficients for 11 Multi-Coefficient Correlation Methods (MCCMs) were optimized against 54 automization energies for molecules composed of C, H, and O atoms containing 343 bonds. It gives two sets of mean errors, the top row is obtained with the SRP coefficients, and the bottom row is obtained with the general parameters.

An embedded-atom potential parametrized to accurate energies of nanoclusters is used to calculate the vapor liquid equilibrium properties of Aluminum. Aluminum saturated vapor phase behaves ideally for T < 2000K, which is needed for the controlled growth of nanoparticles from the vapor phase.

Holthausen has recently provided a comprehensive study of density functional theory for calculating the s/d excitation energies of the 3d transition metal cations. This study did not include the effects of scalar relativistic effects, and we show here that the inclusion of scalar relativistic effects significantly alters the conclusions of the study. We find, contrary to the previous study, that local functionals are more accurate for the excitation energies of 3d transition method cations than hybrid functionals. The most accurate functionals, of the 38 tested, are SLYP, PBE, BP86, PBELYP, and PW91. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [ABSTRACT FROM AUTHOR]

Several semiempirical tight-binding models are parametrized and tested for aluminum clusters and nanoparticles using a data set of 808 accurate AlN (N = 2-177) energies and geometries. The effects of including overlap when solving the secular equation and of incorporating many-body (i.e., nonpairwise) terms in the repulsion and electronic matrix elements are studied. Pairwise orthogonal tight-binding (TB) models are found to be more accurate and their parametrizations more transferable (for particles of different sizes) than both pairwise and many-body nonorthogonal tight-binding models. Many-body terms do not significantly improve the accuracy or transferability of orthogonal TB, whereas some improvement in the nonorthogonal models is observed when many-body terms are included in the electronic Hamiltonian matrix elements.

In previous work we have shown that the PBE0 hybrid density functional method with the MG3 all-electron basis set is an accurate method for calculating the atomization energies of small aluminum clusters (Al2-Al7). However, the MG3 basis set is very expensive for molecules much larger than Al13; therefore, we have developed a new effective core potential (ECP) method for aluminum to reduce the cost of obtaining accurate results for nanoparticles. Our method involves a hybrid of the Stuttgart semiempirical effective core potential and the compact effective potential (CEP) potential, and it uses a newly optimized polarized valence triple-ζ basis set. The combination of the new ECP and the new polarized valence triple-ζ basis set for Al is called the Minnesota effective core (MEC) method for Al. The method was optimized with a training set of atomization energies and geometries for AlH, AlC, AlO, AlCCH, Al2H, Al2C, Al2O, and Al3 and atomization energies of three Al13 structures, and we tested it on six test sets composed of 20 atomization energies for systems as large as Al13. We also present an improved all-electron polarized triple split basis set for oxygen, called 6-311+G(d*,p). For the test sets, the mean unsigned error (MUE) of the new method with respect to PBE0/MG3 is 0.06 eV for atomization energies and 0.007 Å for bond lengths, which constitutes a very significant improvement over the quality of the results that can be obtained with effective core potentials and valence basis sets in the literature (of the eight methods in the literature, the best previous method had average errors of 0.63 eV and 0.036 Å). We have also tested the MEC method with a variety of hybrid density functional theory, hybrid meta density functional theory, and pure GGA and meta GGA functionals and found that the average MUE, relative to each functional with all-electron basis sets, is 0.04 eV for atomization energies and 0.009 Å for bond lengths for the new effective core method and 0.16-0.20 eV and 0.013-0.033 Å for effective core potential and valence basis sets in the literature.