Electron density properties and metallophilic interactions of gold halides AuX2 and Au2X (X = F–I): Ab Initio calculations

We present ab initio calculations of the electron density properties and metallophilic interactions of the gold halide series, AuX₂ and Au₂X (X = F–I) as well as their anions performed at MP2 theoretical level with extended basis sets. The gold halide's structure, stability, and interactions with alkali metal atoms were investigated. The mechanisms of metallophilic interactions were explored by natural bond orbital analyses, electron localization function, electron density deformation, atoms in molecules, and reduced density gradient analyses. © 2016 Wiley Periodicals, Inc.     

The quasiparticle concept in vibrational–electronic problems in molecules. I. Partitioning of the vibrational–electronic Hamiltonian

The partitioning of the vibrational–electronic Hamiltonian is presented. This partitioning is based on a new quasiparticle transformation that is constructed in such a way that the adiabatic approximation is included into the unperturbed Hamiltonian; nonadiabacity, anharmonicity, and electron correlation are treated as perturbations. We also present the second quantization treatment for bosons. The many body perturbation theory expansion for the vibrational–electronic Hamiltonian is suggested. A comparison of this approach is made with gradient techniques.     

Effects of substituents on molecular devices

The current–voltage characteristics of small aliphatic chains of alkanes, alkenes, alkynes, and oligophenylene‐ethylenes, with and without substituents and terminated in sulfur attached nanosized gold electrodes are determined using ab initio procedures for discrete and extended systems in a density functional theory‐Green function's approach where most of the chemistry is considered. It is found that the current–voltage characteristics of small molecules can be tailored by the addition of substituents. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Gold nanoparticles deposited on SiO2/Si100: correlation between size,electron structure,and activity in CO oxidation

Nanosize gold particles were prepared by Ar(+) ion implantation of 10-nm thick gold film deposited onto a SiO(2)/Si(100) wafer possessing no catalytic activity in the CO oxidation. Along with size reduction the valence band of the gold particles and the actual size were determined by ultraviolet- and X-ray photoelectron spectroscopy (UPS, XPS) and by transmission electron microscopy (TEM) as well as atomic force microscopy (AFM), respectively. The catalytic activity was determined in the CO oxidation. Energy distribution of the photoelectrons excited from 5d valence band of gold was strongly affected by Ar(+) implantation. This variation was interpreted by the redistribution of the valence band density of states (DOS). The intrinsic catalytic activity of the gold particles increased with decreasing size. When an Au/FeO(x) interface was created by FeO(x) deposition on large gold nanoparticles, a significant increase in the rate of the CO oxidation was observed. These data can be regarded as an experimental verification of the correlation between the catalytic activity and valence band density of states of gold.     

A new theory of electric conductivity

This theory proposes that electric conductivity, metallic or otherwise, ohmic or superconducting, is simply the result of electron density moving through atomic and molecular orbital overlaps in material bodies. The theory argues that electron density moves without resistance (is superconducting) while it is contained within extended quantum mechanical (QM) states which are constructed so that the electron wave function does not experience reflections at any interface. The theory states that ohmic conduction results when the electron wave function does experience reflections at QM interfaces, and requires the continuous external application of electromotive force (EMF) to overcome those reflections and maintain an electric current.     

Theoretical Study of α‐V2O5‐Based Double‐Wall Nanotubes

First‐principles calculations of the atomic and electronic structure of double‐wall nanotubes (DWNTs) of α‐V₂O₅ are performed. Relaxation of the DWNT structure leads to the formation of two types of local regions: 1) bulk‐type regions and 2) puckering regions. Calculated total density of states (DOS) of DWNTs considerably differ from that of single‐wall nanotubes and the single layer, as well as from the DOS of the bulk and double layer. Small shoulders that appear on edges of valence and conduction bands result in a considerable decrease in the band gaps of the DWNTs (up to 1 eV relative to the single‐layer gaps). The main reason for this effect is the shift of the inner‐ and outer‐wall DOS in opposite directions on the energetic scale. The electron density corresponding to shoulders at the conduction‐band edges is localized on vanadium atoms of the bulk‐type regions, whereas the electron density corresponding to shoulders at the valence‐band edges belongs to oxygen atoms of both regions.     

Hellmann–Feynman theorem near the threshold

The features of the spectrum structure are considered for situations where some parameter λ of the N‐electron Hamiltonian reaches the threshold value η under which the discrete energy level falls into the continuous spectrum. The electron density properties are also studied. It is proved that for a sequence of the wave functions converging in energy to the lower bound of the continuous spectrum as λ approaches η the corresponding sequence of the electron densities converges to the density of the (N ? 1)‐electron ground state. The results generalize the Hellmann–Feynman theorem for the cases where only the one‐side energy derivatives exist or there is no limiting wave function. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Density of states of alternant cyclic polyenes (CH)N by a direct Lanczos method

A direct full configuration interaction approach, previously used for studying individual low-lying eigenvalues, is combined with iterative Lanczos calculations, in order to obtain global properties of large Hermitean Hamiltonian matrices. To this effect systematic generation of random start vectors is used to compute statistical approximations to the density of states (DOS). Applications for cyclic polyenes in order to illustrate the viability of the scheme modeled by correlated, high-binding Pariser-Parr-Pople (PPP) Hamiltonians of increasing complexity are presented. The degree of correlation in the solutions is controlled by the parameter β. Convergence properties of the DOS for N = 10 and N = 14 are studied varying the extent of correlation. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 719–728, 1997     

Green's function formalism coupled with Gaussian broadening of discrete states for quantum transport: application to atomic and molecular wires

A Green's function formalism incorporating broadened density of states (DOS) is proposed for the calculation of electrical conductance. In cluster-molecule-cluster systems, broadened DOS of the clusters are defined as continuous DOS of electrodes and used to calculate Green's function of electrodes. This approach combined with density functional theory is applied to the electrical transmission of gold atomic wires and molecular wires consisting of benzene-1,4-dithiolate, benzene-1,4-dimethanethiolate, 4,4(')-bipyridine, hexane dithiolate, and octane dithiolate. The B3LYP, B3PW91, MPW1PW91, SVWN, and BPW91 functionals with the LANL2DZ, CEP, and SDD basis sets are employed in the calculation of conductance. The width parameter was successfully determined to reproduce the quantum unit of conductance 2e(2)/h in gold atomic wires. The combination of the B3LYP hybrid functional and the CEP-31G basis set is excellent in reproducing measured conductances of molecular wires by Tao et al. [Science 301, 1221 (2003); J. Am. Chem. Soc. 125, 16164 (2003); Nano Lett. 4, 267 (2004)].     

Volume‐dependent potential approach for tungsten

A scheme to produce density‐of‐states‐(DOS)‐dependent potentials for d‐metals on the basis of the local density approximation calculations is suggested. As an example this scheme is applied to construct a DOS‐dependent potential for tungsten. The second moment of the tungsten DOS is calculated. We show that the obtained potentials give a good agreement of cohesive properties with the experimental data. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 71: 343–348, 1999     

Extended states of a shallow donor located near a semiconductor–insulator interface

Scattering of a conduction electron by a charged shallow donor located near a semiconductor–insulator interface in the semiconductor or by a charged center embedded in the insulator is considered within the model of a hydrogenlike atom in a semi-infinite space. The interface influence is allowed for by spatial confinement of the electron envelope wave function. The impurity electrostatic image at the interface is taken into account. The problem is separable in prolate spheroidal coordinates and thus is solvable exactly. A rapidly convergent expansion is proposed for the angular eigenfunctions. The radial eigenfunctions are calculated directly by numerical integration of the radial boundary value problem. Expansions of the scattering wave function and the scattering amplitude in terms of the eigenfunctions of the problem are obtained. Using the extended and localized state wave functions, the photoionization cross section of a shallow donor near a semiconductor–insulator interface is calculated. It is presented as a superposition of the oscillator strengths of transitions to the partial extended eigenstates that constitute the scattering wave function. Near the interface, the cross section is enhanced significantly and redistributed over the direction of photoionized electron escape. The photoionization threshold follows the localized state energy varying with the donor–interface distance. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66 : 435–456, 1998     

Influence of Se and Zn substitution on the electronic transport on a CdTe nanotube-based molecular device: a first-principles study

The electronic transport property of pure cadmium telluride (CdTe) nanotube, selenium-substituted and zinc-substituted CdTe nanotube-based molecular device are investigated with density functional theory. The electronic transport property of CdTe nanotube is studied in terms of device density of states (DOS), electron density, transmission spectrum, and transmission pathways. The substitution of selenium and zinc atoms along the left electrode and bias voltage has the impact in the DOS. The electron density is found to be more at cadmium site in the left electrode. The transmission spectrum provides the insight into the transmission of electrons from valence band to conduction band across CdTe nanotube. The transmission pathway provides the visualization of electron transmission along CdTe nanotube. The results of present work provide a clear vision to tailor CdTe nanostructures with enhanced electronic property with substitution impurity for optoelectronic devices and photovoltaic cells.     

Gold nanoparticles with different capping systems: an electronic and structural XAS analysis

Gold nanoparticles (NPs) have been prepared with three different capping systems: a tetralkylammonium salt, an alkanethiol, and a thiol-derivatized neoglycoconjugate. Also gold NPs supported on a porous TiO(2) substrate have been investigated. X-ray absorption spectroscopy (XAS) has been used to determine the electronic behavior of the different capped/supported systems regarding the electron/hole density of d states. Surface and size effects, as well as the role of the microstructure, have been also studied through an exhaustive analysis of the EXAFS (extended X-ray absorption fine structure) data. Very small gold NPs functionalized with thiol-derivatized molecules show an increase in d-hole density at the gold site due to Au-S charge transfer. This effect is overcoming size effects (which lead to a slightly increase of the d-electron density) for high S:Au atomic ratios and core-shell microstructures where an atomically abrupt Au-S interface likely does not exist. It has been also shown that thiol functionalization of very small gold NPs is introducing a strong distortion as compared to fcc order. To the contrary, electron transfer from reduced support oxides to gold NPs can produce a higher increase in d-electron density at the gold site, as compared to naked gold clusters.     

Length dependence of coherent electron transportation in metal–alkanedithiol–metal and metal–alkanemonothiol–metal junctions

We have applied the elastic-scattering Green’s function theory to study the coherent electron transportation processes in both metal–alkanedithiol–metal (gold–[S(CH₂)_nS]–gold, n = 8–14) and metal–alkanemonothiol–metal (gold–[H(CH₂)_nS]–gold, n = 8–14) at the hybrid density functional theory level. It is shown that the current decreases exponentially with the molecular length. At the low temperature limit the electron decay rate, β, for alkanedithiol junction is found to be around 0.30/CH₂ at 1.0 V bias, much smaller than the calculated value of 0.60/CH₂ for alkanemonothiol junction. The decay rate for alkanedithiol junction at the room temperature is neither sensitive to the activation of the Au–S stretching vibrational mode nor to the external bias. The calculated current–voltage characteristics and decay rates for both junctions are in excellent agreement with the corresponding experimental results.     

Spin‐orbit ZORA and four‐component Dirac–Coulomb estimation of relativistic corrections to isotropic nuclear shieldings and chemical shifts of noble gas dimers

Hartree–Fock and density functional theory with the hybrid B3LYP and general gradient KT2 exchange‐correlation functionals were used for nonrelativistic and relativistic nuclear magnetic shielding calculations of helium, neon, argon, krypton, and xenon dimers and free atoms. Relativistic corrections were calculated with the scalar and spin‐orbit zeroth‐order regular approximation Hamiltonian in combination with the large Slater‐type basis set QZ4P as well as with the four‐component Dirac–Coulomb Hamiltonian using Dyall's acv4z basis sets. The relativistic corrections to the nuclear magnetic shieldings and chemical shifts are combined with nonrelativistic coupled cluster singles and doubles with noniterative triple excitations [CCSD(T)] calculations using the very large polarization‐consistent basis sets aug‐pcSseg‐4 for He, Ne and Ar, aug‐pcSseg‐3 for Kr, and the AQZP basis set for Xe. For the dimers also, zero‐point vibrational (ZPV) corrections are obtained at the CCSD(T) level with the same basis sets were added. Best estimates of the dimer chemical shifts are generated from these nuclear magnetic shieldings and the relative importance of electron correlation, ZPV, and relativistic corrections for the shieldings and chemical shifts is analyzed. © 2015 Wiley Periodicals, Inc.     

Charge transfer between a molecule and an infinite electron reservoir in the MO scheme

A quantitative reference for comparing molecules (and sites of molecules) likely to exchange electrons with a molecular or crystalline partner can be obtained by coupling such molecules to a model electron reservoir with a continuous energy spectrum. In this study the required procedure is defined and mathematically formulated, within the standard orbital scheme. The reservoir is modeled as an infinite linear chain of atoms with one atomic orbital whose coupling is larger than the largest half-bandwidth of the molecules to be compared, coupled by a suitable bond parameter to a specific site of the molecule. The resulting level broadening and local density of states (DOS) are determined using Dyson's equation to get a tractable expansion of the Green function of the molecule-reservoir system. An example of application and a brief discussion of the dependence of the results on the type of Hamiltonian utilized are given. © 1996 John Wiley & Sons, Inc.     

Effects of Ta content on the phase stability and elastic properties of β Ti–Ta alloys from first-principles calculations

The effects of Ta content on the phase stability, the elastic property and the electronic structure of β type Ti–Ta alloys were studied from first-principles calculations based on the density functional theory. It is found that the phase stability, tetragonal shear constant C′, bulk modulus, elastic modulus and shear modulus of β type Ti–Ta alloys increase with the Ta content increasing monotonously. The lowest elastic modulus of the alloys is realized when the valence electron number (e/a) is around 4.25. Moreover, the phase stability of the alloys was discussed based on the calculated density of state (DOS).     

On the connections between Brueckner–coupled-cluster,density-dependent Hartree–Fock,and density functional theory

The existence of an effective one-particle Hamiltonian in the Brueckner coupled cluster model naturally leads to the definition of an effective interaction G, which is a function of the T₂ amplitudes. Two types of approximations to G are proposed: One is purely phenomenological, while the other is based on approximations to the Brueckner T₂ equation. In both cases, the resulting effective interaction may be viewed as electron-density-dependent. Generalizing Hartree–Fock theory to accommodate density-dependent interactions (DDHF ), a method is obtained that is capable of accounting for correlation effects in an independent particle framework. The heuristic Skyrme force, successfully used in nuclear physics to model nucleon–nucleon interactions, is presented here as an example of an effective electron–electron correlation interaction. Due to the δ-function character of the Skyrme force, it is possible to express the energy in this model by an integral over an energy density, thus formally providing a connection between DDHF and density functional theory for this particular case. An approximation to the Brueckner T₂ equation is also proposed in the coordinate representation. In this model, the density-matrix dependence of T₂ is reduced to a nonlocal electron density dependence by means of an expansion which introduces terms that depend on the gradient of the density. The first term in this expansion amounts to a “local density approximation” to Brueckner coupled cluster theory. © 1995 John Wiley & Sons, Inc.