On incorporation of atomic correlation in transition-metal molecular calculations: NiH

The atomic correlation terms necessary to lead to anaccurate 4s²3d⁸-4s^t 3d⁹ separation for the Ni atom have been incorporated into all-electron MC SCF/Cl calculations for the X² Δ state of NiH. The calculated potential curve properties are significantly improved compared to calculations which dissociate to Hartree-Fock atoms.     

Ab initio Hartree–Fock and configuration-interaction treatment of the interaction between two nickel atoms

The interaction between two nickel atoms in the configurations (3d)⁸(4s)² and (3d)⁹ (4s)¹ has been calculated using ab initio methods (Hartree–Fock and configuration interaction). The results of the calculations compare favorably with the optical spectrum. The discrepancy between the calculated and the experimental dissociation energy is discussed, and a new estimate of the dissociation energy is given. The configuration-interaction calculations show that the interaction between the two nickel atoms is of a very complex nature. In spite of this the binding can be interpreted in a simple way. The bond is minly due to the 4sσ_g molecular orbital while the 3d orbitals of the two nuclei are exchange coupled.     

Electronic states of the NiCu molecule determined byab initio Hartree-Fock and configuration interaction methods

The interaction between a Ni atom and a Cu atom in the configurations (3d)⁹(4s)¹ and (3d)¹⁰(4s)¹, respectively, has been calculated usingab initio Hartree-Fock and configuration interaction methods. The chemical bond between the two atoms is due to a bonding 4sσ molecular orbital. Equilibrium distances, dissociation energies and vibrational frequencies are predicted for the low-lying states. Finally the influence of spin-orbit coupling on the low-lying states is considered.     

A matrix-induced change in the electronic ground state of nickel atoms isolated in rare gases

Comparison of the absorption spectra for matrix-isolated Ni atoms with gas-phase data reveals that the electronic ground-state configuration of the isolated atom can be changed by the matrix. While Ni in Ne has the same configuration as in the gas phase, namely 3d⁸4s² we find in Ar, Kr, and Xe the 3d⁹4s¹ configuration to be the ground state. The matrix-induced changes is explained by the repulsive matrix-dopant interaction, which is sufficiently lowered in the 3d⁹4s¹ configuration to overcompensate for the energy difference of 205 cm^?1 by which the 3d⁹4s¹ level lies above the 3d⁸4s² in the free atom.     

A new synthetic route to Mg(2)Na(2)NiH(6) where a [NiH(4)] complex is for the first time stabilized by alkali metal counterions

Mg2Na2NiH6 was synthesized by reacting NaH and Mg2NiH4 at 310 degrees C under hydrogen pressure. The novel structure type was refined from neutron-diffraction data in the orthorhombic space group Pnma (No. 62), with unit cell dimensions of a = 11.428(2), b = 8.442(2), and c = 5.4165(9) Angstrom and a unit cell volume = 523 Angstrom(3) (Z = 4). The structure can be described by (Mg2H2)(2+) layers intersected by (Na2NiH4)(2-) layers. The [NiH4](4-) complex is approximately tetrahedral, indicating formal zerovalent nickel. This is the first example of a solid-state hydride where a [NiH4](4-) complex is directly stabilized by alkali metal ions instead of the more polarizing Mg(2+) ions. A rather long nickel-hydrogen bond distance of 1.65 Angstrom indicates a weaker Ni-H bond as a result of the weaker support from the less polarizing alkali metal counterions.     

Spherically symmetric axial Gaussian lobe 3d and 4f orbitals

The axial Gaussian lobe orbital (AGLO ) representations of 3d and 4f orbitals proposed by LeRouzo and Silvi have been angularly optimized to ensure spherical symmetry of filled 3d and 4f shells. The functions have been tested on the hydrogen atom in the presence of high quality s and p basis sets and found to provide excellent minimal Gaussian representations of polarization functions. Exact orbital degeneracy is not obtained within each shell, however. Tabulated values are given to allow arbitrary scaling of the 3d and 4f lobe mimic orbitals.     

Electronic states of NiFe. Anab initio HF-CI study

Ab initio Hartree-Fock and configuration interaction methods have been employed in describing the interaction between a Ni and an Fe atom. The chemical bond between the atoms is due to a 4sσ molecular orbital. The 3d orbitals merely cause small splittings between the potential energy curves. Equilibrium distance, dissociation energy and vibrational frequency are predicted for the ground state of the molecule.     

A theoretical investigation of the ground and core hole states of linear and bent NiCO; a prototype for CO adsorbed on nickel

Non-empirical LCAO MO SCF calculations within the Hartree-Fock formalism have been performed on linear and bent conformations of NiCO, for both the states arising from the 3d⁹4s¹ and 3d¹⁰ electronic configurations of Ni, for ground and core ionized species. Binding and relaxation energies are computed for the nickel atom, the free ligand (CO) and the absorbed species (NiCO). Comparison with available experimental data reveals good agreement for the shifts in core binding energies for the bent, 3d⁹4s¹ NiCO system. The main contribution to these binding energy shifts is found to be due to relaxation effects, which may be rationalized in terms of atomic population and bond overlap changes accompanying core ionization.     

Compact basis sets for LCAO-LSD calculations. Part I: Method and bases for Sc to Zn

A method for preparing compact orbital and auxiliary basis sets for LCAO-LSD calculations has been developed. The method has been applied to construct basis sets for first row transition metal atoms from Sc to Zn for the 3d^n?14s¹ and 3d^n?24s² configurations. The properties of different expansion patterns have been tested in atomic calculations for the chromium atom.     

An Anomalous Electron Configuration Among 3d Transition Metal Atoms

Physical properties of materials are mainly determined by valence electron configurations, where different valence shells would induce divergent phenomena. In compounds containing Sc²⁺, 3d electron occupancy is expected, the same as other transition metal atoms like Ti³⁺. But this situation still awaits experimental verification in inorganic materials. Here, we selected ScS to measure the valence electron density and orbital population of Sc²⁺ through delicate quantitative convergent-beam electron diffraction. With the absence of 3d orbital features around Sc-atom sites and the nearly bare population of t_2g orbital, the unintuitive occupation of 4s orbital in Sc²⁺ is concluded. It should be the first time to report such a special electron configuration in a transition metal compound, in which 4s rather than 3d orbital is preferred. Our findings reveal the distinct behavior of Sc and probable ways to modulate material properties by controlling electron orbitals.     

Nature of closed‐ and open‐shell interactions between noble metals and rare gas atoms

Interactions between noble metals and rare gases have become an interesting topic over the last few years. In this work, a computational study of the open‐shell (d¹⁰s¹) and closed‐shell (d¹⁰s and d¹⁰s²) noble metals (M = Cu, Ag, and Au) with three heaviest rare gas atoms (Rg = Kr, Xe, and Rn) has been performed. Potential energy curves based on ab initio [MP2, MP4, QCISD, and CCSD(T)] and DFT functionals (M06‐2X and CAM‐B3LYP) were obtained for ionic and neutral AuXe complexes. Dissociation energies indicate that neutral metals have the lowest and cationic metals have the highest affinities for interaction with rare gas atoms. For the same metals, there is a continuous increase in dissociation energies (D_e) from Kr to Rn. The nature of bonding and the trend of D_e and equilibrium bond lengths (R_e) have been interpreted by means of quantum theory of atoms in molecules, natural bond orbital, and energy decomposition analysis. © 2013 Wiley Periodicals, Inc.     

Hydrogen evolution kinetics on Ni cathodes modified by spontaneous deposition of Ag or Cu

Nickel modification by spontaneous deposition of transition metals such as Ag and Cu is shown as an economic and simple alternative for the activation of hydrogen evolution reaction(HER) on cathodes in alkaline media. The kinetics of HER is studied on Ni/Ag and Ni/Cu catalysts by cyclic voltammetry and electrochemical impedance spectroscopy(EIS) using a rotating disk electrode(RDE). Freshly synthesized catalysts, as well as catalysts subjected to a short chronoamperometric ageing procedure, are analyzed and the kinetic and thermodynamic parameters of the HER are obtained. The nickel surface modified with transition metals with an outer shell electronic configuration [xd~(10)(x+1)s~1], such as Cu(3d~(10)4s~1)and Ag(4d~(10)5s~1), shows an improved activity for the HER compared to bare nickel. Furthermore, the Ni/Cu catalyst presents a decreased onset potential. The hydrogen evolution rate, measured as current density at –1.5 V(vs. SCE), is similar on Ni/Cu and Ni/Ag electrodes.     

Theoretical investigation on the GaH molecule and its positive ion

The gallium monohydride (GaH) molecule and its positive ion were theoretically investigated by abinitio molecular orbital calculations with a flexible basis set including g-type functions on the Ga atom. Electron correlations among not only the valence electrons of Ga 4s4p and H 1s but also the semi-core electrons of Ga 3d were incorporated by a size-consistent scheme of the coupled pair approximation. The contribution of the 3d electron correlation was found to be considerable on spectroscopic constants of both GaH and GaH⁺, especially on the bond length. Received: 25 July 1997 / Accepted: 13 November 1997     

Configuration interaction calculations on the 2P ground state of boron atom and C+ using Slater orbitals

Configuration Interaction (CI) calculations on the ground ²P state of boron atom are presented using a wave function expansion constructed with L‐S eigenfunction configurations of s‐, p‐, and d‐Slater orbitals. Two procedures of optimization of the orbital exponents have been investigated. First, CI(SD) calculations including few types of configurations and full optimization of the orbital exponents led to the energy ?24.63704575 a.u. Second, full‐CI (FCI) calculations including a large number of configuration types using a fixed set of orbital exponents for all configurations gave ?24.63405222 a.u. using the basis [4s3p2d] and 2157 configurations, and to an improved result of ?24.64013999 a.u. for 3957 configurations and a [5s4p3d] basis. This last result is better than earlier calculations of Schaefer and Harris (Phys Rev 1968, 167, 67), and compares well with the recent ones from Froese Fischer and Bunge (personal communication). In addition, using the same wave functions, CI calculations of the boron isoelectronic ion C⁺ have been performed obtaining an energy of ?37.41027598 a.u. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

The nickel-group IV molecules NiC,NiSi, and NiGe

All electron ab initio calculations have been applied to elucidate the electronic states and the nature of the chemical bonds in the molecules NiC, NiSi, and NiGe. The calculations have revealed that the ground states of all three molecules are¹Σ⁺, but due to the open 3d shell of the Ni atom the molecules have many low-lying electronic states. The NiC molecule is strongly polar, and the low-lying electronic states have been identified as those arising when the angular momenta of the³F_g Ni⁺ ion are coupled to the angular momenta of the⁴S_uC^? anion. The chemical bond in the NiC molecule has triple bond character due to the valence bond couplings between the Ni 4s and 3dπ electrons and theC 2p electrons. The chemical bonds in the molecules NiSi and NiGe are very much alike; they are double bonds composed of oneσ and oneπ bond. Theσ bond is due to the doubly occupied delocalized molecular orbital composed of the Ni 4s orbital and the Si 3pσ or the Ge 4pσ orbital. Theπ bond originates from the valence bond coupling between the localized hole in the Ni 3dπ orbital and the valencepπ electron of Si or Ge.     

The elements of Flatland: Hartree-Fock atomic ground states in two dimensions for Z = 1–24

The Hartree–Fock problem in two dimensions (2D) has been solved for 1 ≤ Z ≤ 24 using a Gaussian basis and assuming r^?1 Coulomb interactions. The order of occupation of the one-electron states is like in the 3D case. The 1s shell is found to be particularly small and strongly bound, making the 2D hydrogen a “superhalogen” and the 2D He a “superinert gas.” In contrast to 3D, 4s¹3d² and 4s²3d³ configurations are preferred for the 2D “Sc” and “Cu,” respectively. The six first 2D atoms have stronger and the later ones weaker valence-bonding energies than do their 3D analogs. It is noted that the 2D Dirac energy expression for a hydrogenlike atom for m_j = l + 1/2 agrees with the 3D Klein–Gordon one.     

CNDO/2 calculations of relaxation and reconstruction of diamond and silicon [111] surfaces

CNDO /2 calculations have been performed on the clusters X₄H₉ and X₄Y₉ modeling the [111] diamond and silicon surfaces. The X is either carbon or silicon atom and the Y is a pseudoatom containing one sp³ hybrid orbital. It is shown that in the CNDO /2 approximation in the foregoing pseudoatom models, the charge distribution of the cluster is better than the hydrogen atom, because the electronegativity of the hydrogen differs significantly from the electronegativity of the sp² orbital of the silicon atom. Using the CNDO /2 parametrization, the electronegativity of the hydrogen is very near to the electronegativity of the sp³ orbital of the carbon atom, thus the hydrogen can be used for the saturation of the carbon clusters.     

Theoretical study on low-lying electronic states of NiH2

The low-lying electronic states of the NiH2 molecule were investigated by using the MCQDPT2 method. In order to accurately describe the strong correlation derived from the nickel 3d9 super-configuration, a set of diffuse secondary 3d' orbitals were included in the active space, yielding a large active space of 12 electrons in 13 orbitals. It is shown that the absolute minimum energy configuration of NiH2 is bent, in agreement with the experimental observation. The global ground state is 1A1 (or A1 in the spin-orbit coupling case), whereas the lowest linear state is 3Deltag (or 3g). Some other cheaper single-configurational and multi-configurational methods were also used to study both states, and their shortcomings are discussed. Our theoretical results suggest that the arrangement of the experimental frequencies of NiH2 and NiD2 may be incorrect.     

A “double-zeta” type wavefunction for an organometallic: Bis-(π-allyl)nickel

A wavefunction which is of double-zeta quality at the level of the valence orbitals [based on a (11, 7, 5/8, 4/4) gaussian basis set contracted to (4, 3, 2/3, 2/2)] is reported for thebis-(π-allyl)nickel molecule. Independant SCF calculations for two ionized states substantiate the conclusion reached previously for a number of organometallics with a minimal basis set that Koopmans' theorem is not valid for these molecules, namely that the highest occupied orbital from the ground state calculation for the neutral molecule is mostly a ligand π orbital whereas the lowest ionization potential corresponds to the removal of an electron from a molecular orbital which is mostly a metal 3d orbital. The nature of the bonding inbis-(π-allyl)nickel is discussed on the basis of the possible interactions between the metal orbitals and the π orbitals of the allyl group. The interaction between the filled nonbonding π orbital of the allyl group and the empty 3d _xz orbital of the Ni atom appears responsible for most of the bonding, together with some backbonding through an interaction between the 3d x ²?y ²and 3d xyorbitals and the σ and π orbitals of the ligands. The computed value for the rotation barrier about the C-C allyl bond, 90 kcal/mole, rules out this rotation as one of the possible mechanisms which account for the equivalence of the terminal hydrogens in the proton magnetic resonance spectra of π-allyl complexes.     

Structural stability and evolution of terbium-doped silicon clusters and influence of 4f → 5d electronic transition mechanism on magnetism and appearance of photoelectron spectroscopy for TbSin0/− (n = 6-18) clusters

The global minimal structures of terbium-doped Si clusters and their anions TbSi _n^0/− (n = 6-18) are confirmed by employing the ABCluster unbiased global search technique combined with a B2PLYP double-hybrid density functional and comparing consistency of simulated and experimental photoelectron spectroscopy (PES). The results demonstrated that structural evolution patterns for neutral clusters prefer Tb-substitutional to Tb-encapsulated configuration starting from n = 16. While for the corresponding anionic clusters, the growth pattern adopts Tb-linked structures to encapsulated motif. The Natural Population Analysis revealed that the 4f electrons of Tb atom in TbSi _n^0/− (n = 6-18) clusters participate in bonding. The way to participate in bonding is one 4f electron transition to 5d orbital ([Xe]6s²4f⁹ → [Xe]6s²4f⁸5d¹), which significantly affects the cluster's magnetism and appearance of PES. The total magnetic moments of neutral TbSi _n and the corresponding anions maintain at 7 μB and 6 μB, respectively, which are larger than that of an isolated Tb atom. The HOMO-LUMO energy gap, relative stability, and chemical bonding analysis demonstrated that superatomic TbSi₁₆⁻ cluster is a magic cluster with fine thermodynamic and moderate chemical stability.