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Showing papers on "Valence (chemistry) published in 2006"


Journal ArticleDOI
TL;DR: A series of auxiliary basis sets to fit Coulomb potentials for the elements H to Rn (except lanthanides) is presented and computation times for the Coulomb part are reduced by a factor of ca.15 kJ mol(-1) per atom.
Abstract: A series of auxiliary basis sets to fit Coulomb potentials for the elements H to Rn (except lanthanides) is presented. For each element only one auxiliary basis set is needed to approximate Coulomb energies in conjunction with orbital basis sets of split valence, triple zeta valence and quadruple zeta valence quality with errors of typically below ca. 0.15 kJ mol−1 per atom; this was demonstrated in conjunction with the recently developed orbital basis sets of types def2-SV(P), def2-TZVP and def2-QZVPP for a large set of small molecules representing (nearly) each element in all of its common oxidation states. These auxiliary bases are slightly more than three times larger than orbital bases of split valence quality. Compared to non-approximated treatments, computation times for the Coulomb part are reduced by a factor of ca. 8 for def2-SV(P) orbital bases, ca. 25 for def2-TZVP and ca. 100 for def2-QZVPP orbital bases.

4,876 citations


Journal ArticleDOI
TL;DR: Nitrogen doping-induced changes in the electronic properties, defect formation, and surface structure of TiO2 rutile(110) and anatase(101) single crystals were investigated and thermal instability may degrade the catalyst during applications.
Abstract: Nitrogen doping-induced changes in the electronic properties, defect formation, and surface structure of TiO2 rutile(110) and anatase(101) single crystals were investigated. No band gap narrowing is observed, but N doping induces localized N 2p states within the band gap just above the valence band. N is present in a N(III) valence state, which facilitates the formation of oxygen vacancies and Ti 3d band gap states at elevated temperatures. The increased O vacancy formation triggers the 1 x 2 reconstruction of the rutile (110) surface. This thermal instability may degrade the catalyst during applications.

639 citations


Journal ArticleDOI
TL;DR: The all-electron results with quadruple zeta valence basis sets validate semilocal density-functional theory as the workhorse of computational TM chemistry and confirms TPSS as a general purpose functional that works throughout the periodic table.
Abstract: We investigate the performance of contemporary semilocal and hybrid density functionals for bond energetics, structures, dipole moments, and harmonic frequencies of 3d transition-metal (TM) compounds by comparison with gas-phase experiments. Special attention is given to the nonempirical metageneralized gradient approximation (meta-GGA) of Tao, Perdew, Staroverov, and Scuseria (TPSS) [Phys. Rev. Lett. 91, 146401 (2003)], which has been implemented in TURBOMOLE for the present work. Trends and error patterns for classes of homologous compounds are analyzed, including dimers, monohydrides, mononitrides, monoxides, monofluorides, polyatomic oxides and halogenides, carbonyls, and complexes with organic pi ligands such as benzene and cyclopentadienyl. Weakly bound systems such as Ca(2), Mn(2), and Zn(2) are discussed. We propose a reference set of reaction energies for benchmark purposes. Our all-electron results with quadruple zeta valence basis sets validate semilocal density-functional theory as the workhorse of computational TM chemistry. Typical errors in bond energies are substantially larger than in (organic) main group chemistry, however. The Becke-Perdew'86 [Phys. Rev. A 38, 3098 (1988); Phys. Rev. B 33, 8822 (1986)] GGA and the TPSS meta-GGA have the best price/performance ratio, while the TPSS hybrid functional achieves a slightly lower mean absolute error in bond energies. The popular Becke three-parameter hybrid B3LYP underbinds significantly and tends to overestimate bond distances; we give a possible explanation for this. We further show that hybrid mixing does not reduce the width of the error distribution on our reference set. The error of a functional for the s-d transfer energy of a TM atom does not predict its error for TM bond energies and bond lengths. For semilocal functionals, self-interaction error in one- and three-electron bonds appears to be a major source of error in TM reaction energies. Nevertheless, TPSS predicts the correct ground-state symmetry in the vast majority of cases and rarely fails qualitatively. This further confirms TPSS as a general purpose functional that works throughout the periodic table. We also give workstation timing comparisons for the 645-atom protein crambin.

530 citations


Journal ArticleDOI
TL;DR: The ligand field stabilization, the first filling of p orbitals, the transition-metal contraction, and especially the lanthanide contraction are well-reflected by the relative values of the proposed electronegativity.
Abstract: The electronegativities of 82 elements in different valence states and with the most common coordination numbers have been quantitatively calculated on the basis of an effective ionic potential defined by the ionization energy and ionic radius. It is found that for a given cation, the electronegativity increases with increasing oxidation state and decreases with increasing coordination number. For the transition-metal cations, the electronegativity of the low-spin state is higher than that of the high-spin state. The ligand field stabilization, the first filling of p orbitals, the transition-metal contraction, and especially the lanthanide contraction are well-reflected by the relative values of our proposed electronegativity. This new scale is useful for us to estimate some quantities (e.g., the Lewis acid strength for the main group elements and the hydration free energy for the first transition series) and predict the structure and property of materials.

518 citations


Journal ArticleDOI
TL;DR: In this article, the first examples of hyper-deformed structures in nuclei with an axis ratio of 3:1 were presented, in the case of the beryllium isotopes.

345 citations


Journal ArticleDOI
Bjørk Hammer1
TL;DR: In this article, the Hammer-Norskov d-band model was introduced to model the electronic interaction underlying chemisorption at noble and late transition metal surfaces, and the reaction changes described by this model were characterized as an electronic structure effect.
Abstract: An overview of recent advancements in density functional theory modeling of particularly reactive sites at noble and late transition metal surfaces is given. Such special sites include sites at the flat surfaces of thin metal films, sites at stepped surfaces, sites at the metal/oxide interface boundary for oxide-supported metal clusters, and sites at the perimeter of oxide islands grown on metal surfaces. The Newns–Anderson model of the electronic interaction underlying chemisorption is described. This provides the grounds for introducing the Hammer–Norskov d-band model that correlates changes in the energy center of the valence d-band density of states at the surface sites with their ability to form chemisorption bonds. A reactivity change described by this model is characterized as an electronic structure effect. Bronsted plots of energy barriers versus reaction energies are discussed from the surface reaction perspective and are used to analyze the trends in the calculated changes. Deviations in the relation between energy barriers and reaction energies in Bronsted plots are identified as due to atomic structure effects. The reactivity change from pure Pd surfaces to Pd thin films supported on MgO can be assigned to an electronic effect. Likewise for the reactivity change from flat Au surfaces, over Au thin films to Au edges and the Au/MgO interface boundary. The reactivity enhancement at atomic step sites is of both electronic and atomic structure nature for NO dissociation at Ru, Rh and Pd surfaces. The enhancement of the CO oxidation reactivity when moving from a CO+O coadsorption structure on Pt(111) to the PtO2 oxide island edges supported by Pt(111) is, however, identified as mainly an atomic structure effect. As such, it is linked to the occurrence of favorable pathways at the oxide island edges and is occurring despite of stronger adsorbate binding of the oxygen within the oxide edge, i.e. despite of an opposing electronic effect. As a final topic, a discussion is given of the accuracy of density functional theory in conjunction with surface reactions; adsorption, desorption, diffusion, and dissociation. Energy barriers are concluded to be more robust with respect to changes in the exchange-correlation functional than are molecular bond and adsorption energies.

259 citations


Journal ArticleDOI
TL;DR: A giant transfer of spectral weight with distinct features that require an explanation which goes beyond the Peierls transition model as well as the standard single-band Hubbard model is observed.
Abstract: We present a detailed study of the valence and conduction bands of VO2 across the metal-insulator transition using bulk-sensitive photoelectron and O K x-ray absorption spectroscopies. We observe a giant transfer of spectral weight with distinct features that require an explanation which goes beyond the Peierls transition model as well as the standard single-band Hubbard model. Analysis of the symmetry and energies of the bands reveals the decisive role of the V 3d orbital degrees of freedom. Comparison to recent realistic many body calculations shows that much of the k dependence of the self-energy correction can be cast within a dimer model.

255 citations


Journal ArticleDOI
TL;DR: The CD values calculated with MO/DFT are not particularly sensitive to the precise Fe-octahedral geometry, which suggests that a calculated CD is a reasonable approximation in ion adsorption modeling for ill-defined Fe-oxides like HFO and natural Fe oxide materials of soils.

248 citations


Journal ArticleDOI
TL;DR: In this paper, the authors report a systematic examination of band gaps and the nature (covalent or ionic) of bonding in semiconducting 8 and 18-electron half-Heusler compounds through first-principles density functional calculations.
Abstract: Half-Heusler compounds XYZ, also called semi-Heusler compounds, crystallize in the C1b MgAgAs structure, in the space group . We report a systematic examination of band gaps and the nature (covalent or ionic) of bonding in semiconducting 8- and 18-electron half-Heusler compounds through first-principles density functional calculations. We find that the most appropriate description of these compounds from the viewpoint of electronic structures is one of a YZ zinc blende lattice stuffed by the X ion. Simple valence rules are obeyed for bonding in the 8-electron compound. For example, LiMgN can be written Li+ + (MgN)− and (MgN)−, which is isoelectronic with (SiSi), forms a zinc blende lattice. The 18-electron compounds can similarly be considered as obeying valence rules. A semiconductor such as TiCoSb can be written Ti4+ + (CoSb)4−; the latter unit is isoelectronic and isostructural with zinc-blende GaSb. For both the 8- and the 18-electron compounds, when X is fixed as some electropositive cation, the computed band gap varies approximately as the difference in Pauling electronegativities of Y and Z. What is particularly exciting is that this simple idea of a covalently bonded YZ lattice can also be extended to the very important magnetic half-Heusler phases; we describe these as valence compounds, i.e. possessing a band gap at the Fermi energy albeit only in one spin direction. The local moment in these magnetic compounds resides on the X site.

240 citations


Journal ArticleDOI
01 Jul 2006-Micron
TL;DR: EELS measurements on Mn and Fe doped ZnO thin films showed that the valence states of the dopants can unambiguously be determined by calibrating the Mn-L (2,3) and Fe-L(2, 3) ELNES data against the measured standards.

237 citations


Journal ArticleDOI
TL;DR: The catalytic mechanisms of transition-metal compounds during the hydrogen sorption reaction of magnesium-based hydrides were investigated through relevant experiments and found to be influenced by four distinct physico-thermodynamic properties.
Abstract: The catalytic mechanisms of transition-metal compounds during the hydrogen sorption reaction of magnesium-based hydrides were investigated through relevant experiments. Catalytic activity was found to be influenced by four distinct physico-thermodynamic properties of the transition-metal compound: a high number of structural defects, a low stability of the compound, which however has to be high enough to avoid complete reduction of the transition metal under operating conditions, a high valence state of the transition-metal ion within the compound, and a high affinity of the transition-metal ion to hydrogen. On the basis of these results, further optimization of the selection of catalysts for improving sorption properties of magnesium-based hydrides is possible. In addition, utilization of transition-metal compounds as catalysts for other hydrogen storage materials is considered.

Journal ArticleDOI
TL;DR: In this paper, the bond valence model was employed to calculate the bond strength of constituent chemical bonds formed between growth units in both potassium dihydrogen phosphate (KDP) and ammonium dihydric phosphate (ADP) crystals, with the aim to predict and control the crystal shape.

Journal ArticleDOI
01 Apr 2006-Elements
TL;DR: Arsenic has diverse chemical behavior in the natural environment as mentioned in this paper, which is a consequence of the electronic configuration of its valence orbitals, with partially filled states capable of both electron donation and overlap in covalent bonds.
Abstract: Arsenic has diverse chemical behavior in the natural environment. It has the ability to readily change oxidation state and bonding configuration, which creates rich inorganic and organic chemistry. This behavior is a consequence of the electronic configuration of its valence orbitals, with partially filled states capable of both electron donation and overlap in covalent bonds. In natural compounds, arsenic bonds primarily to oxygen and sulfur, generating a variety of aqueous species and minerals. The affinity of arsenic for these two elements, along with its stable bonding to methyl groups, constitutes the structural basis for most organic and biosynthetic compounds. The agile chemistry of arsenic helps to explain its contradictory action as both a toxin and a curative, and its sometimes-elusive behavior in the environment.

Journal ArticleDOI
TL;DR: A dinuclear complex, [(CoTPA)2(DHBQ)](PF6)3, has been successfully synthesized that exhibits a valence tautomeric transition with a distinct hysteresis effect (13 K) around room temperature and photoinduced valencetautomerism under low temperature.
Abstract: A dinuclear complex, [(CoTPA)2(DHBQ)](PF6)3, has been successfully synthesized that exhibits a valence tautomeric transition with a distinct hysteresis effect (13 K) around room temperature and photoinduced valence tautomerism under low temperature.

Journal ArticleDOI
TL;DR: In this paper, the valence, spin, and orbital state of the Co ions in the one-dimensional cobaltate Ca3Co2O6 were investigated using x-ray absorption and magnetic circular dichroism at the Co-L2,3 edges.
Abstract: We have investigated the valence, spin, and orbital state of the Co ions in the one-dimensional cobaltate Ca3Co2O6 using x-ray absorption and x-ray magnetic circular dichroism at the Co-L2,3 edges. The Co ions at both the octahedral Cooct and trigonal Cotrig sites are found to be in a 3+ state. From the analysis of the dichroism we established a low-spin state for the Cooct and a high-spin state with an anomalously large orbital moment of 1.7B at the Co trig ions. This large orbital moment along the c-axis chain and the unusually large magnetocrystalline anisotropy can be traced back to the double occupancy of the d2 orbital in trigonal crystal field.

Journal ArticleDOI
TL;DR: In this article, the authors determine chemical origins of increase in reducibility of CeO2 upon Ti substitution using a combination of experiments and first-principles density functional theory calculations.
Abstract: We determine chemical origins of increase in the reducibility of CeO2 upon Ti substitution using a combination of experiments and first-principles density functional theory calculations. Ce1-xTixO2 (x = 0.0−0.4) prepared by a single step solution combustion method crystallizes in a cubic fluorite structure, confirmed by Rietveld profile analysis. Ce1-xTixO2 can be reduced by hydrogen to a larger extent compared to CeO2 or TiO2. Temperature programmed reduction of CeO2, TiO2, Ce0.75Ti0.25O2 and Ce0.6Ti0.4O2 up to 700 °C in H2 gave CeO1.96, TiO1.92, Ce0.75Ti0.25O1.81, and Ce0.6Ti0.4O1.73, respectively. An extended X-ray absorption fine structure (EXAFS) study of mixed oxides at the Ti K-egde showed that the local coordination of Ti is 4:4, with Ti−O distances of 1.9 and 2.5 A, respectively, which are also confirmed by our first-principles calculations. Bond valence analysis of the microscopic structure and energetics determined from first principles is used to evaluate the strength of binding of different o...

Journal ArticleDOI
TL;DR: The results of this study are used to characterize electrode/electrolyte interfaces of graphite negative electrodes in Li-ion batteries using organic carbonate electrolytes containing LiTFSI or LiBETI salts.
Abstract: X-ray photoelectron valence spectra of lithium salts LiBF4, LiPF6, LiTFSI, and LiBETI have been recorded and analyzed by means of density functional theory (DFT) calculations, with good agreement between experimental and calculated spectra. The results of this study are used to characterize electrode/electrolyte interfaces of graphite negative electrodes in Li-ion batteries using organic carbonate electrolytes containing LiTFSI or LiBETI salts. By a combined X-ray photoelectron spectroscopy (XPS) core peaks/valence analysis, we identify the main constituents of the interface. Differences in the surface layers' composition can be evidenced, depending on whether LiTFSI or LiBETI is used as the lithium salt.

Journal ArticleDOI
TL;DR: A formulation of the n-electron valence state perturbation theory (NEVPT) at the third order of perturbations is presented and the so-called strongly contracted variant of NEVPT, where only a subspace of the first-order interacting space is taken into account, is presented.
Abstract: A formulation of the n-electron valence state perturbation theory (NEVPT) at the third order of perturbation is presented. The present implementation concerns the so-called strongly contracted variant of NEVPT, where only a subspace of the first-order interacting space is taken into account. The resulting strongly contracted NEVPT3 approach is discussed in three test cases: (a) the energy difference between the 3B1 and 1A1 states of the methylene molecule, (b) the potential-energy curve of the N2 molecule ground state, and (c) the chromium dimer (Cr2) ground-state potential-energy profile. Particular attention is devoted to the last case where large basis sets comprising also h orbitals are adopted and where remarkable differences between the second- and third-order results show up.

Journal ArticleDOI
TL;DR: Several molecular cluster compounds that, in their ground states, have unusually largenumbers of unpaired electrons have been prepared, with the highestvaluestodate being S=51/2 fora[Mn].
Abstract: Polynuclear transition-metal clusters in intermediate oxida-tionstatescontinuetoattractgreatattention,mainlybecauseof their fascinating physical properties and the aestheticbeauty and complexity of their structures. An interestingsubareaofthischemistryisthesmallbutgrowingfamilyofmolecules that, in their ground states, have unusually largenumbers of unpaired electrons. Several molecular clustercompoundswithabnormallyhighspin(S)valueshavebeenprepared,withthehighestvaluestodatebeingS=51/2fora[Mn

Journal ArticleDOI
TL;DR: In this article, the structural and electronic properties of the less known bismuth III-V compounds: BBi, AlBi, GaBi, and InBi were analyzed in terms of valence charge density transfer.
Abstract: We have performed ab initio self-consistent calculations based on the full potential linear augmented plane-wave method with the generalized gradient approximation to investigate the structural and the electronic properties of the less known bismuth III-V compounds: BBi, AlBi, GaBi, and InBi. Ground state parameters are computed and compared with available theoretical and experimental works. The zinc-blende phase is found to be the most stable for BBi, AlBi, and GaBi, while InBi prefers the tetragonal PbO structure. The relativistic contraction of the $6s$ orbital of Bi has strong effect on the band structure of III-Bi compounds, which exhibits some features that differ considerably from those of typical III-V semiconductors. In particular, we found an inverted band gap, which reflects a semimetallic character of these systems. Their bonding nature is analyzed in terms of valence charge density transfer, showing three different natures of the bond. Besides, the calculated valence charge density for BBi shows an anomalous behavior characterized by a charge transfer toward the cation B atom, while the others III-Bi behave as the typical III-V compounds with a small charge transfer to the anion bismuth atom.

Journal ArticleDOI
TL;DR: In this paper, the application of the bond valence method for the analysis of ion transport pathways in crystalline cation ion conductors with various mobile cations is reviewed and an extension of the approach to anion conductors is discussed.

Journal ArticleDOI
TL;DR: The use of oxidation number instead of valence can result in misleading descriptions of molecules as discussed by the authors, since the relationship between valence and oxidation number breaks down in many cases, and in such situations, the use of the oxidation number can lead to misleading description of molecules.
Abstract: Terms such as valence, oxidation number, coordination number, formal charge, and number of bonds are widely used throughout chemistry. Although each of these terms has a distinct meaning, their utility is lessened by imprecise usage. Valence, for example, is frequently taken to be synonymous with oxidation number. However, while valence and oxidation number are coincidentally equal for many compounds, the relationship breaks down in many cases; in such situations, the use of oxidation number instead of valence can result in misleading descriptions of molecules. The purpose of this article is to clarify these terms and illustrate how the valence of an atom in a molecule provides a much more meaningful criterion for establishing the chemical reasonableness of a molecule than does the oxidation number.

Journal ArticleDOI
Feiwu Zhang1, Artem R. Oganov1
TL;DR: In this paper, the authors investigated the valence and spin states of iron impurities in the perovskite (Pv) and postperovskites (PPv) polymorphs of MgSiO3 at all lower mantle pressures.

Journal ArticleDOI
TL;DR: The experimental and theoretical results show the existence of attractive interactions between the dopant and O vacancies, and the presence of N embedded in the surface layer reduces the formation energy of O vacancies.
Abstract: The electronic properties of N-doped rutile TiO2(110) have been investigated using synchrotron-based photoemission and density-functional calculations. The doping via N2+ ion bombardment leads to the implantation of N atoms (approximately 5% saturation concentration) that coexist with O vacancies. Ti 2p core level spectra show the formation of Ti3+ and a second partially reduced Ti species with oxidation states between +4 and +3. The valence region of the TiO(2-x)N(y)(110) systems exhibits a broad peak for Ti3+ near the Fermi level and N-induced features above the O 2p valence band that shift the edge up by approximately 0.5 eV. The magnitude of this shift is consistent with the "redshift" observed in the ultraviolet spectrum of N-doped TiO2. The experimental and theoretical results show the existence of attractive interactions between the dopant and O vacancies. First, the presence of N embedded in the surface layer reduces the formation energy of O vacancies. Second, the existence of O vacancies stabilizes the N impurities with respect to N2(g) formation. When oxygen vacancies and N impurities are together there is an electron transfer from the higher energy 3d band of Ti3+ to the lower energy 2p band of the N(2-) impurities.

Journal ArticleDOI
TL;DR: In this paper, the authors carried out self-consistent ab initio calculations within density functional theory using supercell models to understand the detailed electronic structure of deep defect states in narrow band-gap semiconductors.
Abstract: Understanding the detailed electronic structure of deep defect states in narrow band-gap semiconductors has been a challenging problem. Recently, self-consistent ab initio calculations within density functional theory using supercell models have been successful in tackling this problem. In this paper, we carry out such calculations in PbTe, a well-known narrow band-gap semiconductor, for a large class of defects: cationic and anionic substitutional impurities of different valence, and cationic and anionic vacancies. For the cationic defects, we study the chemical trends in the position of defect levels by looking at series of compounds $R{\mathrm{Pb}}_{2n\ensuremath{-}1}{\mathrm{Te}}_{2n}$, where $R$ is vacancy or monovalent, divalent, or trivalent atom. Similarly, for anionic defects, we study compounds $M{\mathrm{Pb}}_{2n}{\mathrm{Te}}_{2n\ensuremath{-}1}$, where $M$ is vacancy, S, Se or I. We find that the density of states near the top of the valence band and the bottom of the conduction band get significantly modified for most of these defects. This suggests that the transport properties of PbTe in the presence of impurities may not always be interpreted by simple carrier doping (from bound impurity states in the gap) concepts, confirming such ideas developed from qualitative and semiquantitative arguments.

Journal ArticleDOI
TL;DR: It is found that the maximum-intensity as well as the Pearson and Walsh-Dray methods show larger relative changes of the ratio between Mn3+ and Mn4+ than curve-fitting, and the Walsh-dray method promises the most accurate determination of small valency shifts.

Journal ArticleDOI
TL;DR: The MP2 calculations corroborate the XeCu bond lengths and predict Xe Cu dissociation energies approximately 50-60 kJ mol(-)(1) and predict valence molecular orbitals with significant shared electron density between Xe and Cu and negative local energy densities at the XECu bond critical points.
Abstract: XeCu covalent bonding has been found in the complexes XeCuF and XeCuCl. The molecules were characterized by Fourier transform microwave spectroscopy, supported by MP2 ab initio calculations. The complexes were prepared by laser ablation of Cu in the presence of Xe and SF6 or Cl2 and stabilized in supersonic jets of Ar. The rotational constants and centrifugal distortion constants show the XeCu bonds to be short and rigid. The 131Xe, Cu, and Cl nuclear quadrupole coupling constants indicate major redistributions of the electron densities of Xe and CuF or CuCl on complex formation which cannot be accounted for by simple electrostatic effects. The MP2 calculations corroborate the XeCu bond lengths and predict XeCu dissociation energies ∼50−60 kJ mol-1. The latter cannot be accounted for in terms of induction energies. The MP2 calculations also predict valence molecular orbitals with significant shared electron density between Xe and Cu and negative local energy densities at the XeCu bond critical points. All...

Journal ArticleDOI
TL;DR: In this paper, the electron energy loss spectroscopy (EELS) technique along with an extensive suite of affined reference spectra were used to determine Cr valence (or at least constrain the possible valences) at high-spatial resolution (tens-of-nanometer scale) across a wide valence range.

Journal ArticleDOI
TL;DR: Chemical bonding in the pentaerythritol tetranitrate crystal based on the experimental electron density obtained from X-ray diffraction data at 100 K and theoretical calculations at the experimental molecular geometry have been analyzed in terms of the Quantum Theory of Atoms in Molecules.
Abstract: Chemical bonding in the pentaerythritol tetranitrate crystal based on the experimental electron density obtained from X-ray diffraction data at 100 K and theoretical calculations at the experimental molecular geometry have been analyzed in terms of the Quantum Theory of Atoms in Molecules. Features of the intra- and intermolecular bond critical points and the oxygen atom lone-pair locations are discussed. Numerous intermolecular bonding interactions, including O···H and O···O, have been found and characterized. Atomic charges and atomic energies were integrated and compared with those for similar compounds. The N−O topological bond orders have been calculated for the first time, and the PETN atomic valences have been estimated.

Journal ArticleDOI
TL;DR: The structures and properties of transition metal oxide (TMO) clusters of the group VIB metals, (MO(3) (M = Cr, Mo, W; n = 1-6), have been studied with density functional theory (DFT) methods and the acid/base properties are expected to play important roles in their catalytic activities.
Abstract: The structures and properties of transition metal oxide (TMO) clusters of the group VIB metals, (MO3)n (M = Cr, Mo, W; n = 1−6), have been studied with density functional theory (DFT) methods. Geometry optimizations and frequency calculations were carried out at the local and nonlocal DFT levels with polarized valence double-ζ quality basis sets, and final energies were calculated at nonlocal DFT levels with polarized valence triple-ζ quality basis sets at the local and nonlocal DFT geometries. Effective core potentials were used to treat the transition metal atoms. Two types of clusters were investigated, the ring and the chain, with the ring being lower in energy. Large ring structures (n > 3) were shown to be fluxional in their out of plane deformations. Long chain structures (n > 3) of (CrO3)n were predicted to be weakly bound complexes of the smaller clusters at the nonlocal DFT levels. For M6O18, two additional isomers were also studied, the cage and the inverted cage. The relative stability of the ...