Abstract: A modified two-centre atomic orbital expansion is proposed for close-coupling calculations of inelastic electronic processes in ion-atom collisions at intermediate energy, and electron transfer cross sections are calculated for H++H and He+H+ collisions. For close collisions, the inclusion of united-atom orbitals in the expansion is shown to be essential for reproducing experimental data as well as earlier calculations based on multi-state molecular orbital or other pseudostate expansions. The convergence of two-state atomic orbital expansion calculations for KK charge transfer is assessed for various asymmetries of the collision system. It is argued that the present expansion is convenient and fast converging over a broad range of collision energies, particularly for close collisions. In another application, K-shell excitation in Ne++O collisions is modelled. At low collision velocities, no deviations from the predictions of 2p pi -2p sigma molecular orbital studies are found even with extended basis sets.

Abstract: The work is concerned with an ab initio calculation of the energy levels of Mn2+ ions in MnF2. The essential idea is the application of an analytic approximation of Watson's SCF procedure to obtain the spin-orbit interaction and the electrostatic parameters for the isolated ions. Crystal field energy levels are then calculated using the nearest-neighbour point-ion approximation. Despite these approximations the results are quite good and indicate that the technique may be of general use as the starting point of more sophisticated calculations on the dn ion in crystals. In addition, the bands at 39010 cm-1, 41340 cm-1 and 43200 cm-1 are interpreted in terms of double exciton transitions, which are in good agreement with experimental findings.

Abstract: The electronic structure of small Cu clusters Cun (n = 2–6) is investigated by an all‐electron SCF calculation. Basis sets for the calculations are chosen with special care. The calculated atomization energy per atom increases almost linearly with the number of the Cu atoms from Cu4 to Cu6, while the bond energy defined as the atomization energy per bond shows a gradual convergence. The band structure of clusters is closely investigated. The absolute value of the orbital energies for the highest occupied 4s‐like orbitals is around 5 eV for Cu4–Cu6, in agreement with the experimental work function (4.65 eV) of the Cu bulk; however the absolute value of the orbital energies for the highest occupied 3d‐like orbitals is around 13 eV, which is much larger than the photoelectronic result of 6.75 eV. In this connection, the importance of the reorganization effect in the d electron ionization is emphasized. It is proposed that the orbital energies of the 3d‐like orbitals should be shifted by ∼6 eV to compare them...

Abstract: I Quanta and Molecules: The Quantum Theory of Planck, Einstein and Nernst.- I.1 The Law of Blackbody Radiation.- I.2 The Significance of the Constants in Planck's Law.- I.3 Fluctuations and Light-Quanta.- I.4 Energy-Quanta and the Derivations from Classical Theories.- I.5 The Search for Other Quantum Phenomena.- I.6 Specific Heats, New Quantum Hypotheses and the First Solvay Conference.- I.7 The Consolidation of Quantum Theory.- II The Bohr-Sommerfeld Theory of Atomic Structure.- II.1 The Spectra of Atoms and Molecules: The Empirical Foundations.- II.2 Ideas Towards a Model of Atomic Structure.- II.3 Niels Bohr and the Origin of the Quantum Theory of Line Spectra.- II.4 Atoms as Conditionally Periodic Quantum Systems.- II.5 Three Principles of Atomic Theory.- III The Bohr Festival in Gottingen.- III.1 The Gottingen Tradition of Mathematics and Physics.- III.2 The Continuity of the Tradition: Richard Courant, Max Born and James Franck in Gottingen.- III.3 Progress in Atomic Models from 1913 to 1921.- III.4 Bohr's Wolfskehl Lectures and the Theory of the Periodic System of Elements.- III.5 Immediate Impact and Triumph of Bohr's Theory of the Periodic System of Elements.- IV The Mechanical and Spectroscopic Failures of Atomic Models.- IV.1 Wolfgang Pauli's Background and Early Scientific Work.- IV.2 The Helium Atom and Other Few-Body Problems.- IV.3 The Magnetic Anomaly and the Stern-Gerlach Effect.- IV.4 The Anomalous Zeeman Effect.- IV.5 The Breakdown of the Bohr-Sommerfeld Theory: Anomalous Zeeman Effects and the Crossed-Field Problem.- V The Problems of Radiation Theory.- V.1 The Proof of the Light-Quantum Hypothesis.- V.2 The Bohr-Kramers-Slater Theory of Radiation.- V.3 Bose's Light-Quantum Statistics and Its Extension to Gas Theory.- V.4 The Phase Waves Associated with Matter.- V.5 The Status of the Radiation Problem in 1925.- VI New Methods and Concepts in Atomic Theory.- VI.1 The Dispersion-Theoretic Approach.- VI.2 Atomic Structure and the Problem of Closed Electron Shells.- VI.3 The Rule for Equivalent Electrons: Pauli's Exclusion Principle.- VI.4 The Discovery of Electron Spin.- Epilogue.- References.- Author Index.

Abstract: Electron capture from atomic hydrogen into orbitals of fully stripped ions (helium to boron) is investigated at impact velocities between 0.3 and 1.4 au. The authors report the summed total cross sections for electron capture into the states of the incident nucleus, obtained by solution of the time-dependent Schrodinger equation in terms of a basis set of the Hylleraas type with a straight-line approximation for the nuclear motion.

Abstract: The electronic structure of small Cu clusters Cun (n = 2–6) is investigated by an all‐electron SCF calculation. Basis sets for the calculations are chosen with special care. The calculated atomization energy per atom increases almost linearly with the number of the Cu atoms from Cu4 to Cu6, while the bond energy defined as the atomization energy per bond shows a gradual convergence. The band structure of clusters is closely investigated. The absolute value of the orbital energies for the highest occupied 4s‐like orbitals is around 5 eV for Cu4–Cu6, in agreement with the experimental work function (4.65 eV) of the Cu bulk; however the absolute value of the orbital energies for the highest occupied 3d‐like orbitals is around 13 eV, which is much larger than the photoelectronic result of 6.75 eV. In this connection, the importance of the reorganization effect in the d electron ionization is emphasized. It is proposed that the orbital energies of the 3d‐like orbitals should be shifted by ∼6 eV to compare them...

Abstract: A modified two-centre atomic orbital expansion is employed in a study of charge transfer in Li3++H collisions at 7Li impact energies E=14=140 keV Cross sections are calculated for transitions into individual Li2+ orbitals as well as into all bound orbitals The calculated total transfer cross sections are in excellent agreement with existing experimental data but differ significantly from those of other model descriptions

Abstract: On the basis of the Heisenberg equation of motion and the Linderberg–Seamans approximations, useful formulas for, β-resonance integrals in the all-valence NDO-like semiempirical methods have been derived. The case of s, p, d basis sets of atomic orbitals has been considered.

Abstract: Anisotropies observed in collisional deexcitation of laser excited Na atoms are analysed in terms of the density matrix describing the Na(3P) atom after the process Na(32 S)+e −(E)→Na(32 P)+e −(E−δE). Collision energiesE range from 5.1 to 22.1 eV, and scattering angles fromθ col=0 to 25°. The results are presented with reference to a coordinate frame in which the angular momentum transferred during collision is parallel to the quantization axis. This choice allows a convenient exploitation of reflection symmetry and offers most direct relation of measurable quantities to the sublevel excitation amplitudes as e.g. computed by close coupling and distorted wave methods. Comparison between experiment and theory provides a sensitive probe of the strengths and shortcomings of the theory when predicting these alignment and orientation parameters. Since we discuss a complete set of data containing all accessible information on the atomic orbital the present measurements allow the detection of a deviation from coherence in the excitation for small scattering anglesθ col≈5–10° atE=5.1 eV which we attribute to electron exchange.

Abstract: A model is proposed that quantitatively accounts for the moment variation in transition metal–metalloid (T–M) crystals and glasses. The model, formulated from the valence bond theory, assumes that each Co atom surrounding an M atom contributes a d orbital to participate in p–d hybrid bonding. The hybridized d orbital is then considered to be nonmagnetic. Hence the moment variation in Co–M alloys is determined by the local symmetry of the M atom and not by the valence of M. The moment reduction is caused by orbital transfer rather than charge transfer. Excellent quantitative agreement is found when the model is compared with experimental data for crystalline and amorphous Co–M alloys. It is found that amorphous alloys retain the same local environment around the metalloid atom as in the crystalline cases and that the bonding is equivalent. The bond model predicts zero moment change for dilute bcc Fe alloys because the bonding levels in the Fe band have no uncompensated spin. Reasonable agreement with exper...

Abstract: A new state of CuO, labelled Y2Σ+, predicted by ab initio calculations, has been observed in an infrared transition with the X2Πi ground state at 7800 cm-1 (λ = 1.3 μm). Significant population of the new Y state was achieved via collisional transfer from the A2Σ state, itself populated by c.w. dye-laser pumping. From ab initio calculations, it is shown that the Y2Σ+ and X2Πi states from an unique perturber pair interacting on oxygen centered 2pσ-2pπ orbitals. In the frame of this interpretation, the theoretical magnitude of the X2Π1/2 Λ-type splitting deduced from the ab initio wavefunctions is in good agreement with the spectroscopic value. It fixes a positive sign for the corresponding p parameter and determines definitively the electronic parities of all the 2Σ levels of CuO.

Abstract: The electronic structure of amorphous CuxZr1-x (x=0.65, 0.50 and 0.35) alloys is calculated for realistic, structurally relaxed models by using the linear muffin-tin orbital method in the atomic sphere approximation and the recursion method. The orbitals of the Cu 3d and 4s and the Zr 4d and 5s electrons are included in the calculation and the electronic charge density is determined self-consistently. The hybridised mixing between the Cu 3d and Zr 4d states can be seen and the calculated density of states agrees well with the observed XPS and UPS data. The observed change of the Zr-Zr distance depending on the Cu contents is attributed to charge transfer into the Zr 4d band.

Abstract: A real-space molecular-orbital description of electronic wave functions which are postulated to be the precursors of the superconducting state in high- and low-dimensional metals is presented, based on self-consistent X-alpha scattered-wave (SCF-X alpha-SW) molecular-orbital calculations for clusters representing the local molecular environments in these materials. It is shown that there is a persistent correlation between the occurrence of superconductivity in a material and the existence of spatially delocalized molecular orbitals at the Fermi energy which are bonding within and antibonding between 'layers' or 'tubes' of overlapping atomic orbitals that span many atoms, forming a type of 'electron network' at the Fermi energy, as exemplified by P pi 'layered' molecular-orbital topologies in Al and (TMTSF)2PF6, and by d sigma 'tabular' molecular-orbital topologies in Nb and Nb3Sn. This description of the precursor superconducting state is consistent with the original conjectures of London that the superconducting-state wave function is 'molecular' in nature, 'rigid' in character, and of wide spatial extent, from which observed physical properties (e.g., diamagnetism and nondissipative electrical currents) of the superconducting state logically follow.

Abstract: Recent progress in the description of electron processes in slow ion-atom collisions with atomic expansion models has stimulated interest in trajectory effects in those studies. The author discusses a reformulation of the atomic expansion method, explicitly taking into account curved-line internuclear trajectories. As a first application, total charge transfer cross sections in C6++H collisions for energies E=0.1-1.0 keV amu-1 are found to be considerably reduced in curved-line trajectory calculations from those derived with straight-line trajectories.

Abstract: The mechanism for near‐threshold photon‐stimulated desorption (PSD) and electron‐stimulated desorption (ESD) is examined theoretically using finite cluster, quantum chemical techniques to model the interaction of a hydrogen atom with a metal surface. Configuration interaction calculations on clusters modeling both the 〈100〉 and 〈111〉 faces of an fcc crystal yield a consistent picture of the process. A band of strongly repulsive states which asymptotically dissociate to ions is found to lie ∠25 eV above the ground state. This excitation energy is consistent with the threshold observed in ESD and PSD experiments on the 〈100〉 surfaces of Ni and Pd. The states of this band all involve double excitations from the metal–hydrogen bonding orbitals.

Abstract: We shall provide here a brief survey of the relevant background quantum mechanics that is required for the chemical bonding treatment presented in this book. In general, we shall state only the main results, without any derivation of them. Much, if not all of this material could be familiar to many readers. For fuller treatments, the reader should consult some of the numerous standard texts on quantum mechanics and valence.

Abstract: Experimental binary (e, 2e) energy spectra of fluoroethylene are presented and compared with Green's function calculations. Electron momentum distributions of outer and inner valence orbitals have also been measured and are discussed in conjunction with the theoretical results. The information obtained allows a full analysis of the molecular orbital symmetry and of the nature of the chemical bond in fluoroethylene.

Abstract: A synthesis of Hartree-Fock and spin density functional theories yields a fully correlated many-electron energy minimisation method which avoids orbital self-interaction without requiring the use of localised orbitals. The new method is designed primarily for use with extended systems and may facilitate calculation of the band structure of semiconductors and insulators.

Abstract: The evolution of first principles theories capable of describing the electronic structure of actinide compounds is reviewed. Particular emphasis is placed upon molecular orbital and cluster models for gas phase and solid state systems respectively. Comparisons are made between “direct” methods based upon Dirac-Fock (DF) and local density Dirac-Slater (DS) schemes, and “indirect” pseudopotential or perturbative schemes. Prospects for basing a full many-electron treatment upon the self-consistent DS single particle orbitals are discussed. The nature and magnitude of relativistic effects on chemical bonding and valence electron level structures have been subjects of perennial interest. DF studies on heavy atom hydrides, using a one-center expansion technique, have been used to study the relativistic contraction of bond lengths. Early beliefs that the bond contraction was simply due to contraction of the underlying atomic orbitals; i.e. an overlap effect, have turned out to be incorrect. Recent results which throw light on this aspect are discussed. The development of reliable pseudopotential methods in a relativistic framework gives hope that rather large systems (both in terms of atomic number, and number of nuclear sites) can be treated by considering only valence electron states explicitly. It is possible at present to carry out all-electron calculations on actinide complexes in local density models, so interesting comparisons between direct and indirect methods become feasible. Self-consistent DS energy levels and charge distributions are presented for a number of (AcOm)q complexes, where Ac=Th,U,Np, Pu, representative of oxide compounds and spectroscopically accessible “free” complexes. An effort is made to correlate the f-electron occupation and bonding interactions to the variables; coordination number, formal valency, and bond lengths. The magnetization density in UO2 is discussed, and preliminary results on some halide compounds are presented.