Prediction Of Electronic Structure Research Articles

The permanent electric dipole moments and magnetic hyperfine interactions of ruthenium mononitride, RuN

The low rotational features of the (0,0) F 2Σ+←X 2Σ+ band system of a supersonic molecular beam of RuN have been recorded at high spectral resolution via laser induced fluorescence spectroscopy. The electric field induced dependence of the P11(1) and Q21R(0) branch features of the RuN104 isotopomer were analyzed to produce permanent electric dipole moments, μ, of 1.89(5) and 1.07(5) D for the X 2Σ+ and F 2Σ+ states, respectively. The splitting in the field free spectrum of the RuN101 isotopomer was analyzed to produce a Fermi contact, bF(X 2Σ+), parameter of −0.0349(4) cm−1. The results are interpreted using the electronic structure predictions for the F 2Σ+ and X 2Σ+ states given by Ram et al. [J. Chem. Phys. 109, 6329 (1998)] and compared with RuC and FeC.

Metal Complexes of Allyl Derivatives of C60 Fullerene: Molecular and Electronic Structure Prediction from Density Functional Calculations.

The problem of existence of η3—π-complexes of C60 fullerene with transition metal atoms is discussed. The complexes C60R3Co(CO)3 (R = H, F, Cl, Br), C60H3NiCp, and C60H3Fe(CO)Cp, where C60R3 is an allyl derivative of C60 fullerene, were shown to be sufficiently stable. In these complexes the metal atoms are η3—π-bound to the fullerene cage. In contrast to this, the metal atoms in the C60H3Li and C60H3FeCp complexes are η5—π-coordinated to the carbon cage. Density functional calculations were carried out with the Perdew—Burke—Ernzerhof exchange-correlation potential (PBE). It was concluded that the type of bonding in the complexes of allyl derivatives of C60 fullerene depends on the nature of the species attached. Among the systems studied, the maximum energy of the η3—π-bond was obtained for the C60H3NiCp complex. The results obtained can be useful in the design of synthesis of new fullerene derivatives with the η3—π-coordination of the transition metal atoms to the carbon cage.

Metal complexes of allyl derivatives of C60 fullerene: molecular and electronic structure prediction from density functional calculations

The problem of existence of η3—π-complexes of C60 fullerene with transition metal atoms is discussed. The complexes C60R3Co(CO)3 (R = H, F, Cl, Br), C60H3NiCp, and C60H3Fe(CO)Cp, where C60R3 is an allyl derivative of C60 fullerene, were shown to be sufficiently stable. In these complexes the metal atoms are η3—π-bound to the fullerene cage. In contrast to this, the metal atoms in the C60H3Li and C60H3FeCp complexes are η5—π-coordinated to the carbon cage. Density functional calculations were carried out with the Perdew—Burke—Ernzerhof exchange-correlation potential (PBE). It was concluded that the type of bonding in the complexes of allyl derivatives of C60 fullerene depends on the nature of the species attached. Among the systems studied, the maximum energy of the η3—π-bond was obtained for the C60H3NiCp complex. The results obtained can be useful in the design of synthesis of new fullerene derivatives with the η3—π-coordination of the transition metal atoms to the carbon cage.

Ab initio molecular dynamics simulation of LiBr association in water

A computationally economical scheme which unifies the density functional description of an ionic solute and the classical description of a solvent was developed. The density functional part of the scheme comprises Car–Parrinello and related formalisms. The substantial saving in the computer time is achieved by performing the ab initio molecular dynamics of the solute electronic structure in a relatively small basis set constructed from lowest energy Kohn–Sham orbitals calculated for a single anion in vacuum, instead of using plane wave basis. The methodology permits simulation of an ionic solution for longer time scales while keeping accuracy in the prediction of the solute electronic structure. As an example the association of the Li+–Br− ion-pair system in water is studied. The results of the combined molecular dynamics simulation are compared with that obtained from the classical simulation with ion-ion interaction described by the pair potential of Born–Huggins–Mayer type. The comparison reveals an important role played by the polarization of the Br− ion in the dynamics of ion pair association.

Ab Initio Simulation of Metal Cluster Surrounded by Electrolyte

An effective and computationally economical scheme, which unifies density functional description of a metal electronic structure and the classical molecular dynamics description of an electrolyte in contact with the metal, is described. The density functional part of the scheme comprises Car‐Parinello and related formalisms. This scheme allows the extension to longer time scale of the simulation of metal‐electrolyte interface while keeping fairly good accuracy in the prediction of the metal electronic structure. The numerical scheme is implemented in the relatively simple model of a metal cluster surrounded by an electrolyte. The elementary event of an atom leaving a metal surface as an ion stabilized by solvent molecules has been studied. In particular the potential of mean force of the ion as it dissolves was evaluated. The evolution of the solvation shell of the ion as it leaves the surface is calculated as a further example. © 2000 The Electrochemical Society. All rights reserved.

Sandwich complexes of Si, Ge, Sn, and Pb with cyclopentadienyl type derivatives of corannulene and fullerene C60: stability estimates and molecular and electronic structure prediction by the MNDO/PM3 method

The ability of cyclopentadienyl type derivatives of corannulene C20H10 and fullereneIh-C60 to form η5-π-complexes and the problem of their existence is discussed. MNDO/PM3 calculations of half-sandwich complexes η5-π-MC20H15, η5-π-MC20H15+, η5-π-MC60H5, η5-π-MC60H5 and sandwich complexes 2η5-π-M(C20H15)2, 2η5-π-M(C20H15)2, 2η5-π-M(C60H5)2 (M=Si, Ge, Sn, Pb) were performed. For all systems studied, local minima were found on corresponding potential energy surfaces and the heats of formation, geometric parameters, and distributions of effective atomic charges were calculated. Sandwich complexes are most likely to exist with M=Si and Ge. The energy and geometric characteristics of η5-π-complexes of corannulene were compared with those of η5-π-complexes of fullereneIh-C60. It was concluded that the results of quantum-chemical calculations of sandwich type corannulene derivatives can be used for simulation of the geometry and electronic structure of analogous complexes of fullereneIh-C60.

Strong crystal field effect in - optical absorption study

=-1 Results of optical absorption measurements in polarized light on tetravalent neptunium diluted in a single crystal are reported. The recorded spectra are complex, pointing to the presence of an impurity. The electronic transitions assigned to the ion are interpreted in terms of the usual model, following the actual understanding of the neptunium electronic structure and independent theoretical predictions. R.m.s. deviations of the order of have been obtained for 42 levels fitted with 11 free parameters. The crystal field effect resulting from the fitting is considerably larger than that observed for the uranium ion in the same host.

EPR Spectroscopic and Theoretical Study of Chromium(I) Carbonyl Phosphine and Phosphonite Complexes

Isotropic and frozen-solution EPR spectra are reported for several Cr(I) carbonyl complexes of the type cis-[Cr(CO)4L2]+, mer- and fac-[Cr(CO)3L3]+, and trans-[Cr(CO)2L4]+, where L is a monodentate (or L2 a bidentate) phosphine or phosphonite ligand. Extended Hückel molecular orbital theory calculations were performed for cis- and trans-[Cr(CO)4L2], mer- and fac-[Cr(CO)3L3], and cis- and trans-[Cr(CO)2L4] (L = PH3, P(OH)3). The EPR results are discussed in light of the electronic structure predictions, which also provide some insights on the oxidation potentials and the isomerization reaction energetics of these complexes. Isotropic 31P hyperfine couplings can be understood in terms of spin densities in the Cr 3d, P 3s, and P 3p orbitals.

Models for the Molybdenum(VI/V) Centers of the Molybdenum Hydroxylases and Related Enzymes. Geometry, Electronic Structure, and EPR g-Tensor Predictions from ab Initio and Semiempirical Molecular Orbital Studies

The geometries and electronic structures of several molybdenum(V) and molybdenum(VI) complexes with tetradentate N 2 S 2 and N 2 O 2 ligands (LH 2 =N,N'-bis(2-mercaptophenyl)-N,N'-dimethyl- 1,2-diaminoethane, N,N'-bis(2-hydroxyphenyl)-N,N'-dimethyl-1,2-diaminoethane) which have been proposed as models for the molybdenum-(VI/V) centers of the molybdenum hydroxylases and related enzymes have been predicted using ab initio and INDO molecular orbital methods. Ab initio and INDO geometrical predictions have been compared with known X-ray crystal structures for three complexes and have been found to be in excellent agreement. In addition, the EPR g tensors of the molybdenum(V) complexes have been estimated using INDO methods

Shell Structure in Photoionization Spectra of Trivalent Metal Clusters

AbstractPhotoionization mass spectra of large AlN and InN clusters, produced by laser vaporization technique, have been recorded via standard TOF spectroscopic methods. Ionization potentials are measured in the size range N = 37–112 for aluminum and N = 31–132 for indium. Comparison between these two trivalent simple metals is presented, as well as with the electronic shell structure predictions of the spherical jellium model. In the large size range N = 200–1400, regular oscillations are observed in the AlN mass spectra. This oscillating behaviour, which is a manifestation of the electronic shell structure of the Ne = 3N valence electrons, is analyzed within the semiclassical theory of single‐particle quantum level density. The oscillation period as a function of Ne3, two times shorter than the period obtained in alkali cluster experiments, is well explained by the classical two‐turn star orbit contribution, whereas for alkali metals the electronic structure near the Fermi energy is governed by the single‐turn triangular and square orbit contributions.

Pulsed growth and electronic structure of layered CuFe films on Cu(100)

The authors have attempted the preparation of CuFe superlattice structures by pulsed metal deposition in an atomic layer-by-layer fashion upon a Cu(100) substrate at 300 K. The electronic structure of a single crystal 6*(1 ML Fe:1 ML Cu)(100)CuFe film has been probed by angle-resolved ultraviolet photoemission spectroscopy. Experimental photoemission results have been critically compared with both fully self-consistent linear muffin-tin orbital (LMTO) predictions of the ground state electronic structure and with photocurrent calculations using time reversed LEED formalism. Theoretical predictions indicate the expected large rearrangements in the valence electron states which are shown to be large enough in certain E(k) points to provide a definite 'fingerprint' of superlattice formation. Despite LEED/AES measurements which indicate a high quality p(1*1) single crystal film exhibiting strong compositional modulation they show by comparing experimental and theoretical angle-resolved photoemission spectra that the attempted Brillouin zone folding in the growth direction has not been imposed. Their result suggests that formation of metallic superlattice with short repeat periods (2 ML) is a nontrivial task despite the apparent ideality of the CuFe system for this purpose. Results presented here are supportive of nonideality in the growth mechanism of Fe/Cu(100).

Molecular conformation and electronic structure of 1,1'-bipyrrole. an ab initio approach

Internal rotation about the N-N ' interannular bond of 1,1'-bipyrrole has been investigated by means of STO-3G and 4-31G ab initio calculations. A perpendicular disposition of the pyrrole rings is predicted as the most stable conformation. The highest occupied π MOs of 1,1'-bipyrrole are correlated with those of pyrrole and their evolution with the twisting angle is analyzed. Electronic structure predictions are in good agreement with experimental photoelectron spectral data.

Advances in research on clusters of transition metal atoms

This article reviews research on the physical and chemical properties of clusters of transition metal atoms, with special emphasis on recent advances made through the new molecular beam and flow techniques. Following our introductory section describing motivation for the study of metal clusters, we outline the major synthetic techniques: Matrix isolation or suspension and free-jet or cold flow condensation of laser-vaporization plasmas. Before discussing the new experiments based on these methods, we review physical and chemical models of transition metal clusters. These models are adaptations of bulk or molecular descriptions of metals or metal containing compounds, and are concerned with the prediction of electronic structure and elementary excitation in clusters, magnetic order and structural rigidity, or chemical reactivity and perturbations. Within this framework we survey recent experimental measurements and their interpretations. Highlighted examples include: (1) the precision measurement of rovibronic or magnetic properties of dimers and trimers as tests of computational electronic structure approximations, (2) measurements of electron binding energies of Fe and Ni clusters as a probe of the molecular versus bulk behavior of these systems, (3) the current status of experiments on the optical properties of small metallic particles, (4) magnetic moment measurements on Fe clusters as critical tests of the molecular theory of metallic and magnetic behavior, (5) discussion of possible effects of cluster melting, and the melting of Au clusters, (6) the facile size-selected reactions of free Fe and Ni clusters with H 2, 0 2 and CO, and (7) the evidence for new chemistry in the adsorption of hydrocarbons on free Pt. Ir and Ru clusters.

Approximate molecular orbital theory: the ese mo formalism. II. Direct comparison with ab initio results

The utility of the ESE MO formalism is examined in relation to ab initio results, when a typical small gaussian basis is employed. Good electronic structure predictions result from simplified schemes based on the ESE MO formalism, despite adverse features of the chosen basis set, for the diverse group of molecules FH, OH 2, NH 3, FCN, O 3 and OF 2.

Prospects for further considerable extension of the periodic table

Considers the prediction of chemical properties and electronic structure of transactinide elements, and the search, synthesis, and predicted nuclear stability of superheavy elements.