Geometrical and electronic structure of small copper nanoclusters: XANES and DFT analysis

The geometrical and electronic structure of small copper nanoclusters was studied by density functional theory (DFT) and analysis of X-ray absorption spectra. It was shown that the icosahedral geometry of small copper nanoclusters of 13 atoms was energetically more stable than cuboctahedral geometry. The binding energies in these structures were compared; the theoretical XANES spectra were compared with experiment. The paper gives the results of ab initio calculations of the electronic structure of copper clusters differing in size.     

Non-covalent Interactions and Charge Transfer between Propene and Neutral Yttrium-Doped and Pure Gold Clusters

The dopant and size-dependent propene adsorption on neutral gold (Au_n) and yttrium-doped gold (Au_n−1Y) clusters in the n=5–15 size range are investigated, combining mass spectrometry and gas phase reactions in a low-pressure collision cell and density functional theory calculations. The adsorption energies, extracted from the experimental data using an RRKM analysis, show a similar size dependence as the quantum chemical results and are in the range of ≈0.6–1.2 eV. Yttrium doping significantly alters the propene adsorption energies for n=5, 12 and 13. Chemical bonding and energy decomposition analysis showed that there is no covalent bond between the cluster and propene, and that charge transfer and other non-covalent interactions are dominant. The natural charges, Wiberg bond indices, and the importance of charge transfer all support an electron donation/back-donation mechanism for the adsorption. Yttrium plays a significant role not only in the propene binding energy, but also in the chemical bonding in the cluster-propene adduct. Propene preferentially binds to yttrium in small clusters (n<10), and to a gold atom at larger sizes. Besides charge transfer, relaxation also plays an important role, illustrating the non-local effect of the yttrium dopant. It is shown that the frontier molecular orbitals of the clusters determine the chemical bonding, in line with the molecular-like electronic structure of metal clusters.     

Electronic structure of NH+: An ab initio study

We report ab initio self‐consistent field MRSD‐CI electronic structure calculations of the NH⁺ cation. A basis set of DZ + POL quality augmented with Rydberg and bond functions was employed together with an extensive treatment of electron correlation. More than 50 electronic states of NH⁺ are reported, including doublets, quartets, and sextets. Leading configurations, vertical ionization energies of NH, vertical excitation energies of NH⁺, and potential energy curves are reported. Spectroscopic properties calculated for the known bound electronic states of NH⁺ are found in good agreement with experiment. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Comparison of electronic structure development in gold clusters formed on amorphous and annealed carbon substrates

The growth of gold clusters vacuum deposited onto differently prepared carbon surfaces was studied by UV photoclectron spectroscopy. Variable photon energies were used to follow the evolution of band structure with cluster size. The development of electronic structure is markedly different for clusters formed on amorphous and annealed carbon substrates.     

Chain structure and stiffness of Teflon AF glassy amorphous fluoropolymers

The structure of the amorphous perfluorinated polymer Teflon AF 2400 and other structurally close perfluoropolymers was studied by means of a quantum chemistry method. The electronic and structural characteristics of the repeating unit and polymer models with ten and nine monomer units were obtained. It was found that two nonplanar isomers can exist for different models of the perfluorinated dioxole ring with a difference of their energy minimums of 10.8 kJ/mol. The orthogonal-block structure of the polymer chain of the perfluorodioxole homopolymer and its copolymer with tetrafluoroethylene was proposed, the block size was found, and a possible diameter of the void formed by two neighboring polymer chains was evaluated. Potential energy curves for the rotation of certain chain fragments about different bonds of the polymer main chain were constructed, and the polymer stiffness was shown to substantially depend on the molar ratio between perfluorodioxole and tetrafluoroethylene units in the copolymer and on the geometry of the perfluorodioxole ring.     

Effect of metal centres and substituents on the structure and optoelectronic properties of diarylethene compounds: A theoretical study

Diarylethene derivatives are a class of fascinating photochromic materials because of their open and closed isomers with different absorption spectra and many other characteristics.To reveal the detailed structure and optoelectronic properties as well as the effect of metal centres and substituents on them,a systematic study on a series of diarylethene derivatives and their Re(I),Pt(II),and Ir(III) complexes was performed via theoretical calculation.The optimized geometries,electronic properties,frontier molecular orbitals,ionization potentials,electron affinities,reorganization energies,and absorption spectra for both of their open-and closed-isomers have been calculated and analyzed.Metal-coordination and substituents exhibit great influence on the photophysical,charge-injection and-transporting characteristics.In addition,the binding of F-with the boron atom of dimesitylboryl group through Lewis acid/base interactions also induces great changes of structural,photophysical and electronic properties for these diarylethene derivatives,and consequently the compound with the substituent of dimesitylboryl group can be used as selective near-infrared phosphorescent F-probe.     

Molecular structure and electronic spectrum of taspine: Semiempirical calculations

AM1 calculations show that taspine has the three energy-minima along the rotation-like nuclear displacement of the dimethylaminoethyl group. They correspond to two enantiomeric structures and a Cs structure, which have nearly equal energies. The energy barrier between the enantiomeric structures and the Cs structure is calculated to be about 1 kcal/mol. The small barrier readily causes an intramolecular interconversion of the two enantiomers through the Cs structure and thus results in the optical inactivity of taspine. CNDO/S calculations show that the electronic spectra of the enantiomer and the Cs structure are quite similar. These calculated spectra are in good agreement with the observed electronic spectra.     

The band structure of one-dimensional (tetrazaporphyrinato)cobalt(II). A semi-empirical self-consistent field crystal orbital analysis

The band structure of (tetraporphyrinato)cobalt(II) (2) has been investigated by means of a semi-empirical INDO (intermediate neglect of differential overlap) crystal orbital approach. The simplest stoichiometric unit of the title compound contains an uneven number of electrons. We have considered metallic and insulating (Mott) electronic distributions in the “half-filled” band. The Hartree-Fock energies for two spatial symmetries have been determined: (i) singly occupied Co 3d_z² band (a_1g) and (ii) singly occupied ligand-centered (a_1u) linear combination. The mean-field energies of insulating “Mott” states have been calculated by means of a grand canonical (GC) averaging procedure. The electronic ground state is of spatial A_1g symmetry (“half-filled” Co 3d_z² dispersion) and corresponds to an insulating band occupation. The calculated width of the a_1g dispersion amounts to 0.13 eV. It is argued that the band structure results of 2 are in qualitative agreement with available experimental results derived for (phthalocyaninato(cobalt(II).     

Quantum chemical investigation of the electronic structure of poly(2,4-dioxocyclobuta-1,3-diylidene)

The electronic structure of poly(2,4-dioxocyclobuta-1,3-diylidene) molecule is calculated by the semiempirical CNDO/S3 method. The calculated Wiberg indices and the additive occupancies of interatomic bonds determine the structural formula, which includes the C=C and C=O conjugated double bonds and corresponds to the name of the compound. Polarization of C=O bonds and πelectron conjugation do not lead to a zwitterionic structure with positive aromatic fourmembered cycles. The indices and occupancies of carboncarbon bonds 1– 3 and 2– 4 are σelectronic, negative, and negligibly small. The band structure corresponds to strong electronaccepting properties of the polymer; the MO of the bottom of the lowlying vacant band contains 2pπorbitals of all atoms of the compound. The occupied π-electronic bands do not overlap, and their widths are relatively small. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 5, pp. 781–786, September–October, 1998.     

The role of disorder on the electronic structure of conjugated polymers. The case of poly-2,5-bis(phenylethynyl)-1,3,4-thiadiazole

Insight into the electronic structure of disordered poly-2,5-bis(phenylethynyl)-1,3,4-thiadiazole in an amorphous region, in comparison to an ideal two-planar cofacial oligomer system, is pursued. The atomic structure of the amorphous polymer was obtained from classical molecular dynamics. It was subsequently used to calculate the electronic states and inter- and intrachain electronic coupling integrals using the density functional theory based charge patching method. The interchain electronic coupling integrals in the amorphous system were found to be an order of magnitude smaller than in the ordered system with similar distances between the chains. The results also suggest that the electronic structure of the whole system cannot be understood as a collection of the electronic structures of individual chains. The band gap of the whole system is significantly smaller than the band gaps of individual chains. This decrease originates from the disordered long range electrostatic potential created by the dipole moments of polymer repeat units, which should be minimized if one seeks good transport properties.     

Electronic structure and vertical excitation spectrum of methylene amidogen CH2N

Ab initio electronic structure calculations are reported for five electronic states of the methylene amidogen radical. Structure parameters for the ground electronic state are predicted by RHF and D -MBPT (4) calculations. Vertical excitation energies were determined using four different theoretical chemical models: complete active space (CAS ) MCSCF , CAS /MCSCF plus singles and doubles Cl, fourth-order many-body perturbation theory SDQ -MBPT (4), and coupled-cluster theory.     

2-[(1H-benzimidazol-2-ylmethyl)-amino]-benzoic acid methyl ester: crystal structure, DFT calculations and biological activity evaluation

In the present study, structural properties of 2-[(1H-benzimidazol-2-ylmethyl)-amino]-benzoic acid methyl ester have been studied extensively by spectral methods and X-ray crystallography. Quantum mechanical calculations of energies, geometries, vibrational wavenumbers, NMR and electronic transitions were carried out by DFT using B3LYP functional combined with 6-31G(d) basis set. Natural bond orbitals (NBO) analysis and frontier molecular orbitals were performed at the same level of theory. DFT calculations showed good agreement between the theoretical and experimental values of optimized and X-ray structure as well as between the vibrational and NMR spectroscopy. The title compound was screened for its antibacterial activity referring to Tetracycline as standard antibacterial agent.     

Electronic structure of LaF+ and LaF from frozen-core four-component relativistic multiconfigurational quasidegenerate perturbation theory

The electronic structure of the molecules LaF+ and LaF was studied using frozen-core four-component multiconfigurational quasidegenerate perturbation theory. To obtain proper excitation energies for LaF+, it was essential to include electronic correlations between the outermost valence electrons (4f, 5d, and 6s) and ionic core electrons composed of (4s, 4p, 4d, 5s, and 5p). The lowest-lying 16 excited states were examined for LaF+, and the lowest 30 states were examined for LaF. The excitation energies calculated for LaF+ agree with the available experimental values, as well as with values from ligand field theory. Errors are within 0.4 eV; for example, the highest observed state 2Pi is 3.77 eV above the ground state, and the present value is 4.09 eV. For LaF, agreement between the experimental and theoretical state assignments and between the experimental and calculated excitation energies was generally good, except for the electron configurations of certain states. Errors are within 0.4 eV except for a single anomaly; for example, the highest observed excited-state discussed in this work is 2.80 eV above the ground state, and the present value is 2.42 eV. We discuss the characteristics of the bonding in LaF+ and LaF.     

Vibronic structure of jet-cooled 2,6-dimethylbenzyl radical: revisited

We reexamined the vibronic structure of the jet-cooled 2,6-dimethylbenzyl radical that was generated from 1,2,3-trimethylbenzene seeded in a large amount of inert carrier gas helium using a pinhole-type glass nozzle in a corona excited supersonic expansion, from which the vibronically resolved emission spectrum was recorded with a long path double monochromator in the visible region. The spectrum exhibited bands arising from not only the D1 --> D0 transition but also the D2 --> D0 transition, in which transitions the accurate electronic energies of the D2 and D1 states and the revised vibrational mode frequencies in the ground electronic state were obtained by comparison with those from the known data of the precursor and an ab initio calculation.     

A theoretical CNDO CI study of the electronic spectrum and structure of a spiropyran

The electronic structure and spectrum of a model compound of a spiropyran were investigated using an all valence-electrons CNDO CI method. The π → π^* electronic excitations are localized on a given half of the molecule. The photochromic process is discussed on the basis of charge densities and bond orders.     

Competition between van der Waals and hydrogen bonding interactions: structure of the trans-1-naphthol/N(2) cluster

The excitation energy in the multiphoton ionization spectrum of the trans-1-naphthol/N(2) cluster shows only a small red shift with respect to isolated naphthol, indicating a van der Waals pi-bound structure rather than a hydrogen-bonded one. To confirm this interpretation, high-level electronic structure calculations were performed for several pi- and hydrogen-bonded isomers of this cluster. The calculations were carried out at the second order M?ller-Plesset (MP2) level of perturbation theory with the family of correlation consistent basis sets up to quintuple-zeta quality including corrections for the basis set superposition error and extrapolation to the MP2 complete basis set (CBS) limit. We report the optimal geometries, vibrational frequencies, and binding energies (D(e)), also corrected for harmonic zero-point energies (D(0)), for three energetically low-lying isomers. In all calculations the lowest energy structure was found to be an isomer with the N(2) molecule bound to the pi-system of the naphthol ring carrying the OH group. In the CBS limit its dissociation energy was computed to be D(0) = 2.67 kcal/mol (934 cm(-1)) as compared to D(0) = 1.28 kcal/mol (448 cm(-1)) for the H-bound structure. The electronic structure calculations therefore confirm the assignment of the experimental electronic spectrum corresponding to a van der Waals pi-bound structure. The energetic stabilization of the pi-bound isomer with respect to the hydrogen-bonded one is rather unexpected when compared with previous findings in related systems, in particular phenol/N(2).     

Tuning the electronic structure of diboradiferrocenes

A series of diboradiferrocenes with different aryl substituents was prepared through reaction of B,B-dichlorodiboradiferrocene with arylcopper and Grignard reagents. The mesityl and pentafluorophenyl derivatives, - and -, were fully characterized by multinuclear NMR, MALDI-TOF mass spectrometry and X-ray crystallography, and their electronic structure was examined by UV-visible spectroscopy and cyclic voltammetry. A comparison of the data for - and - with those of the parent compound - revealed the importance of electronic and steric effects of the substituents on the electronic structure of the compounds and ultimately the degree of electronic interaction between the two ferrocene moieties. An unusually large redox splitting of DeltaE = 703 mV was determined from the cyclic voltammogram of -.     

Two synthesis routes of organometallic precursors for the elaboration of SiCNYO pre‐alloyed nanopowders

Two routes were simultaneously investigated to prepare organometallic precursors. They were characterized by NMR and FTIR techniques. In the first route, yttrium acetate was silylated by trimethylchlorosilane before its dissolution in hexamethydisilazane. That leads to a liquid precursor containing Si? C? N? Y? O? H elements. In the second route, a precursor with the same elements was elaborated by dissolution of an amminolysed yttrium compound in tetramethyldisiloxane. The amminolysed yttrium compound was obtained through the amminolysis of the yttrium trichloride by triethylamine [N(C₂H₅)₃]. Copyright © 2010 John Wiley & Sons, Ltd.     

Valence-band electronic structure of iron phthalocyanine: an experimental and theoretical photoelectron spectroscopy study

The electronic structure of iron phthalocyanine (FePc) in the valence region was examined within a joint theoretical-experimental collaboration. Particular emphasis was placed on the determination of the energy position of the Fe 3d levels in proximity of the highest occupied molecular orbital (HOMO). Photoelectron spectroscopy (PES) measurements were performed on FePc in gas phase at several photon energies in the interval between 21 and 150 eV. Significant variations of the relative intensities were observed, indicating a different elemental and atomic orbital composition of the highest lying spectral features. The electronic structure of a single FePc molecule was first computed by quantum chemical calculations by means of density functional theory (DFT). The hybrid Becke 3-parameter, Lee, Yang and Parr (B3LYP) functional and the semilocal 1996 functional of Perdew, Burke and Ernzerhof (PBE) of the generalized gradient approximation (GGA-)type, exchange-correlation functionals were used. The DFT/B3LYP calculations find that the HOMO is a doubly occupied π-type orbital formed by the carbon 2p electrons, and the HOMO-1 is a mixing of carbon 2p and iron 3d electrons. In contrast, the DFT/PBE calculations find an iron 3d contribution in the HOMO. The experimental photoelectron spectra of the valence band taken at different energies were simulated by means of the Gelius model, taking into account the atomic subshell photoionization cross sections. Moreover, calculations of the electronic structure of FePc using the GGA+U method were performed, where the strong correlations of the Fe 3d electronic states were incorporated through the Hubbard model. Through a comparison with our quantum chemical calculations we find that the best agreement with the experimental results is obtained for a U(eff) value of 5 eV.     

Ultraviolet spectra and structure of the isomeric dihydroxy- and diamino-substituted benzenes

The semi-empirical all-valence-electron SCF-LCAO-MO-CI method in its Del Bene and Jaffé formalism has been applied to the study of the electronic absorption spectra and structure of isomeric dihydroxy- and diamino-substituted benzenes. The calculated π-π^* singlet excitation energies and corresponding oscillator strengths have been compared with earlier π-electron results and discussed in the light of experimental findings. Ionization potentials, electron affinities, ground-state atomic orbital populations and net electronic charges of atoms, have also been presented.