The molecular and electronic structure of N,N′-ethylenebis(acetylacetonylideiminato)oxovanadium(IV) and the electronic structure of its thio analogue

The electronic structures of the title complexes—VO(acen) and VS(acen)—and the free H₂(acen) ligand are probed using gas-phase UV-photoelectron spectroscopy [acen = N,N′-ethylenebis(acetylacetonylideiminato)]. The effect of the different axial donors on the metal center is examined, as is the effect that the oxo and thio ligands have on the acen orbitals. We find that the oxo and thio donors primarily affect the metal center and that the ligand periphery remains mostly unchanged.     

Structures and electron affinity of XO30,−, XOF40,− and XO2F20,− (X = P,As, Sb,Bi): a theoretical study of novel superhalogen formulae and exceptions of superhalogen formulae

Most superhalogen species are in the form of oxides or halides. To enrich the family of superhalogen species, herein, we investigated the structures and electron affinity (EA) values of higher group 15 elements (X = P, As, Sb, Bi) oxyfluoride species XO₃^0,?, XOF₄^0,? and XO₂F₂^0,?, at the CCSD(T)/aug-cc-pVTZ-pp &; aug-cc-pVTZ //B3LYP/aug-cc-pVTZ-pp &; aug-cc-pVTZ levels (aug-cc-pVTZ-pp for X = Sb and Bi). Some oxyfluoride species, i.e., PO₂F₂^0,?, AsO₂F₂^0,?, SbO₂F₂^0,?, POF₄^0,?, AsOF₄^0,?, SbOF₄^0,? and BiOF₄^0,?, were found to possess higher EA (VDE: 5.0–6.2 eV; ADE: 4.5–5.5 eV) than halogens (F: 3.4 eV; Cl: 3.6 eV). Thus, we recommended that the oxyfluorides in the form of XO₂F₂^0,? and XOF₄^0,? should be considered as potential superhalogens, which have not been considered previously. Surprisingly, we showed that BiO₃ and BiO₂F₂, in superhalogen formulae, possess a high vertical detachment energy (VDE) yet a low adiabatic detachment energy (ADE). This is in marked contrast to the previously reported superhalogens, which generally contain both the high VDE and high ADE values. It is the first report about exceptions of superhalogen formulae. These findings revealed that for the analogous main-group compounds with the same structural formula, the difference in the metallic property of the core element could lead to the significant difference in the ground structures of either the anionic or neutral structures, which would result in the much differed superhalogen features.     

First principles prediction of the elastic,electronic and optical properties of Sn3X4 (X = P,As, Sb,Bi) compounds: Potential photovoltaic absorbers

We report a first-principles study of structural, mechanical and optoelectronic properties of the Sn₃X₄ (X = P, As, Sb, Bi) compounds. The calculations were performed using the full-potential linearized augmented plane wave approach (FP-LAPW). The structural and mechanical properties of Sn₃X₄ (X = P, As, Sb, Bi) compounds were obtained using GGA-PBE. In addition, The Tran-Blaha modified Becke-Johnson exchange potential (TB-mBJGGA) technique was used to calculated the optoelectronic properties. The calculated electronic band structures and density of states reveal a direct band gap at Γ points varied from 0.11 eV to 1.23 eV for X = P, As, Sb, Bi. The optical absorption calculations show that all compounds have high absorption coefficients about twenty times greater than that of CuInSe₂ and CdTe in the visible region. The high absorption of these materials could be attributed to the localized p-states of cation (X = P, As, Sb, Bi) in the lower region of the conduction band.     

Tunable electronic properties and carrier mobility in binary pnictogen nanosheets,PX (X = As,Sb, and Bi)

Catalytic graphitization of kraft lignin to nano-materials was investigated over four transitional metal catalysts (Ni, Cu, Fe, and Mo) through a thermal treatment process under an argon flow at 1000 °C. The catalytic thermal process was examined using thermal gravimetric analysis (TGA) and temperature-programmed decomposition (TPD) experiments. The crystal structure and morphology of the thermal-treated metal-lignin samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. Catalytic graphitization of kraft lignin to nano-materials was investigated over four transitional metal catalysts (Ni, Cu, Fe, and Mo) through a catalytic thermal treatment process. It was observed that multi-layer graphene-encapsulated metal nanoparticles were the main products, beside along with some graphene sheets/flakes. The particle sizes and graphene shell layers were significantly affected by the promoted metals. BET surface areas of samples obtained from different metal precursors were in the range of 88–115 m²/g within the order of Ni-?>?Fe-?>?Mo-?>?Cu-. Thermal gravimetric analysis (TGA) and temperature-programmed decomposition (TPD) experimental results showed that adding transitional metals could promote the decomposition and carbonization of kraft lignin. The catalytic activity increased with an order of Mo?Cu?<?Ni?Fe. XRD results show that face-centered cubic (fcc) Cu crystals is formed in the thermal-treated Cu-lignin sample, fcc nickel phase for the Ni-lignin sample, β-Mo₂C hexagonal phase for the Mo-lignin sample and α-Fe, γ-iron, and cementite(Fe₃C) for the Fe-lignin sample. Average particle sizes of these crystal phases calculated using the Scherrer formula are 52.4 nm, 56.2 nm, 21.0 nm, 23.3 nm, 11.3 nm, and 32.8 nm for Ni, Cu, β-Mo₂C, α-Fe, γ-iron, and Fe₃C, respectively. Raman results prove that the graphitization activity of these four metals is in the order of Cu?<?Mo?<?Ni?<?Fe. Metal properties such as catalytic activity, carbon solubility, and tendency of metal carbide formation were related to the graphene-based structure formation during catalytic graphitization of kraft lignin process.

     

Phase transitions of YbX (X = P,As and Sb) with a NaCl-type structure at high pressures

The powder X-ray diffraction of YbX (X?=?P, As and Sb) with a NaCl-type structure has been studied with synchrotron radiation up to 63?GPa at room temperature. YbSb undergoes the first-order structural phase transition from the NaCl-type (B1) to the CsCl-type (B2) structure at around 13?GPa. The structural change to the B2 structure occurs with the volume collapse of about 1% at 13?GPa. The transition pressure of YbSb is surprisingly lower than that of any other heavier LnSb (Ln?=?Dy, Ho, Er, Tm and Lu). The pressure-induced phase transitions in YbP and YbAs are observed at around 51?GPa and 52?GPa respectively. The transition pressure of both compounds is much higher than that of YbSb. The high-pressure structural behaviour of YbX (X?=?P, As and Sb) is discussed. The volume versus pressure curve for YbX with the NaCl-type structure is fitted by a Birch equation of state. The bulk moduli of these compounds with the NaCl-type structure are 104?GPa for YbP, 85?GPa for YbAs and 52?GPa for YbSb.     

The structural,electronic, and magnetic properties of SrFeOn（n=2 and 2.5）： a GGA＋U study

Using density-functional calculations within the generalized gradient approximation (GGA)+U framework,we investigate the structural,electronic,and magnetic properties of the ground states of SrFeOn (n = 2 and 2.5).The magnetism calculations show that the ground states of both SrFeO2 and SrFeO2.5 have G type antiferromagnetic ordering,with indirect band gaps of 0.89 and 0.79 eV,respectively.The electronic structure calculations demonstrate that Fe cations are in the high-spin state of (dz2 )2(dxz,dyz)2(dxy)1(dx2 y2 )1(S = 2),unlike the previous prediction of (dxz,dyz)3(dxy)1(dz2 )1(dx2 y2 )1(S = 2) for SrFeO2,and in the high-spin state of (dxy,dxz,dyz,dx2 y2 ,dz2 )5(S = 5/2) for SrFeO2.5.     

The role of Sb(5+) in the structure of Sb(2)O(3)-B(2)O(3) binary glasses--an NMR and Mössbauer spectroscopy study

Glasses of general formula xSb₂O₃ (1−x)B₂O₃ (0x0.8) have been prepared by conventional melt- quenching. Mössbauer spectroscopy shows that a fraction of the Sb³⁺ is converted to Sb⁵⁺ and this fraction increases with x. High-field ¹¹B MAS NMR gives well-resolved resonances from boron atoms which are 3- and 4-coordinated to oxygen. The fraction of 4-coordinated boron, N₄, goes through a maximum value of 0.12±0.01 at x=0.5. The position of the maximum in N₄ is consistent with the cation potential for Sb³⁺, as observed for other systems. However, the low value of N₄ at this maximum is not so readily explained. The values are similar to those predicted if [BO₄]⁻ were stabilised by [SbO₄]⁺ but the trends with composition are different.     

Short-range order and its effect on the electronic structure of binary alloys: CuZn — a case study

We discuss an application of the generalized augmented space method introduced by one of us combined with the recursion method of Haydock et al (GASR) to the study of electronic structure and optical properties of random binary alloys. As an example, we have taken the 50-50 CuZn alloy, where neutron scattering indicates the existence of short-range order.      

Competition between σ-hole pnicogen bond and π-hole tetrel bond in complexes of CF2=CFZH2 (Z = P,As, and Sb)

ABSTRACT

A computational study of the complexes formed by F₂C=CFZH₂ (Z?=?P, As, and Sb) and F₂C=CFPF₂ with two Lewis bases (NH₃ and NMe₃) has been carried out. In general, two minima complexes are found, one with a σ-hole pnicogen bond and the other one with a π-hole tetrel bond in most complexes but two σ-hole pnicogen bonded complexes are obtained for F₂C=CFZH₂ and NH₃. They have similar stability though F₂C=CFSbH₂ engages in a much stronger σ-hole pnicogen bond with NMe₃. The –PF₂ substitution makes the π-hole on the terminal carbon form a tetrel bond with NH₃. A heavier –ZH₂ group engages in a stronger σ-hole pnicogen bond but results in a weaker π-hole tetrel bond. Other than electrostatic interaction, the stability of both complexes is attributed to the charge transfer from the N lone pair into the C–Z/H–Z anti-bonding orbital in the pnicogen bond and the C=C anti-bonding orbital in the tetrel bond.

The σ-hole pnicogen bonded and π-hole tetrel bonded complexes between F₂C=CFZH₂ (Z = P, As, and Sb) and two Lewis bases (NH₃ and NMe₃) have been compared. The results indicate that both interactions can compete, dependent on the nature of the N base.     

Magnetic and electronic properties of hexairon(III) nanocluster with cyclic structure: a Mössbauer study

A molecular cluster containing a coplanar ring of iron(III) ions with spin 5/2 was investigated by Mössbauer spectroscopy. The iron spins are antiferromagnetically coupled so that the ground state has total spin S=0. Spectra in the absence of an applied magnetic field consisted of a quadrupolar doublet, the linewidth of which monotonically increased with the temperature. A quadrupolar splitting of about 0.35 mm/s was found. Calculations of the ironorbital electronic populations were carried out and the quadrupolar splitting was estimated. Its value was in agreement with the experimental one. In addition, the trend of the linewidth was explained in terms of isotropic spin fluctuations. Spectra in the presence of a 4.5 T longitudinal magnetic field were also collected. The hyperfine field was obtained from their fitting. Differences with respect to the hyperfine field obtained from susceptibility data were also interpreted in terms of spin fluctuations.     

High-pressure studies on electronic and mechanical properties of FeBO3 (B = Ti,Mn, Cr) ceramics – a first-principles study

Using the density functional theory (DFT) method, the electronic and mechanical properties of perovskites FeBO₃ (B = Ti, Mn, Cr) nanostructures were studied in the pressure range of 0–100 GPa. The band structure studies show the change in the band structure upon substitution of different B cation in FeBO₃ perovskite structure. The density of states spectrum gives the perception of change in the electronic properties of FeBO₃ with the substitution of B cation. The bulk, shear and Young's moduli were calculated and an increase in the moduli is noticed. Moreover, the hardness increases under high pressure. The high-pressure studies of FeBO₃ perovskite nanostructures are explored at atomistic level. The findings show that ductility and hardness of FeBO₃ get increased upon an increase in the applied pressure. The substitution of Ti, Mn and Cr on FeBO₃ shows a significant change in the electronic and mechanical properties.     

Ab-initio study of structural,electronic, elastic and mechanical properties of RuAl1−xGax (x=0, 0.25, 0.50, 0.75 and 1)

We have used special quasirandom structure to study the structural, electronic, elastic and mechanical properties of RuAl_1−xGa_x alloys for different compositions (x=0, 0.25, 0.50, 0.75 and 1) using a FP-LAPW method based on Density Functional Theory. The exchange and correlation potential is treated within the generalized gradient approximation. Ground state properties such as lattice constant (a₀), bulk modulus (B), its pressure derivative (B′) and elastic constants are calculated. The ductility of these alloys has been analyzed by calculating the ratio of B/G_H, Cauchy pressure (C₁₂–C₄₄) and Frantsevich rule. From this study RuAl and RuGa are found to be brittle, but their alloys show ductile behavior; RuAl_0.50Ga_0.50 is found to be most ductile. Mechanical properties such as Poisson's ratio (σ), Young's moduli (E), and the ratio of elastic anisotropy factor (A) are estimated. We have also correlated the ductility and bonding behavior of these alloys.     

A first-principles study of the properties of P-43m-Si3×2 (X = N,P and As)

The new P-43m-Si₃P₂ and P-43m-Si₃As₂ structures are predicted using the first-principles approach based density functional theory (DFT). The elastic constants, structural stability, phonon dispersion spectra, band structures, density of states, and optical properties of P-43m-Si₃×₂ (X=N, P and As) have been analyzed. The values of the elastic constants indicate that their structures are mechanically stable. Each elastic constant of the Si₃N₂ is greater than the corresponding elastic constants of Si₃P₂ and Si₃As₂. The Young's moduli, shear moduli, bulk moduli, Pugh ratios and Poisson's ratios of P-43m-Si₃×₂ are calculated at 0 GPa. Si₃N₂ has a larger Young's modulus, so it has higher hardness and good resistance to deformation. The bulk moduli of P-43m-Si₃×₂ are isotropic. The shear modulus of Si₃As₂ is anisotropic. The Pugh ratios of P-43m-Si₃×₂ are 0.50, 0.49 and 0.39, respectively. Their Poisson's ratios are 0.28, 0.29 and 0.33, respectively. The results show that they are brittle materials at zero pressure. The calculated phonon spectra confirm that they are dynamically stable. The calculated enthalpy of formation indicates their thermodynamic stability. The energy band gaps of P-43m-Si₃×₂ calculated by HSE06 hybrid function are 0.786, 0.955 and 0.343 eV, respectively. Si₃N₂ has a direct bandgap, Si₃P₂ and Si₃As₂ have indirect bandgaps. The dielectric functions, refractive indices, optical reflectance spectra, absorption coefficients, conductivities and loss functions of P-43m-Si₃×₂ are calculated. The calculated static dielectric constants of P-43m-Si₃×₂ are 5.207, 9.237 and 10.072, respectively. The maximum values of the loss functions of P-43m-Si₃×₂ are 6.408, 5.672 and 5.276 eV, respectively.     

Geometrical,electronic, and magnetic properties of CunFe (n=1–12) clusters: A density functional study

The geometrical, electronic, and magnetic properties of small Cu_nFe (n=1–12) clusters have been investigated by using density functional method B3LYP and LanL2DZ basis set. The structural search reveals that Fe atoms in low-energy Cu_nFe isomers tend to occupy the position with the maximum coordination number. The ground state Cu_nFe clusters possess planar structure for n=2–5 and three-dimensional (3D) structure for n=6–12. The electronic properties of Cu_nFe clusters are analyzed through the averaged binding energy, the second-order energy difference and HOMO–LUMO energy gap. It is found that the magic numbers of stability are 1, 3, 7 and 9 for the ground state Cu_nFe clusters. The energy gap of Fe-encapsulated cage clusters is smaller than that of other configurations. The Cu₅Fe and Cu₇Fe clusters have a very large energy gap (>2.4 eV). The vertical ionization potential (VIP), electron affinity (EA) and photoelectron spectra are also calculated and simulated theoretically for all the ground-state clusters. The magnetic moment analyses for the ground-state Cu_nFe clusters show that Fe atom can enhance the magnetic moment of the host cluster and carries most of the total magnetic moment.     

The spectroscopy of 22Al: a βp, β2p and βα emitter

In an experiment at the LISE3 facility of GANIL, we produced the proton-rich isotope ²²Al by the fragmentation of a ³⁶Ar primary beam at 95 MeV/nucleon. After implantation in a detector telescope, the decay of ²²Al via β-delayed proton emission, β-delayed two-proton emission as well as, for the first time, via β-delayed α emission has been studied. An α peak has been observed at (3.27 ± 0.04) MeV with a branching ratio of (0.31 ± 0.09) %. The comparison of the different decay channels to those of the mirror nucleus ²²F and to shell-model calculations favor a 3⁺ state as being the ground state of ²²Al. A half life of T_1/2 = (59 ± 3) ms has been measured.     

The local and electronic structures of Al90FexCe10−x alloys (x=3, 5, 7): XANES analysis

The x-ray absorption near-edge structure (XANES) of Al₉₀Fe_xCe_10?x (x=3, 5, 7) is measured above the Fe K edge and analyzed theoretically by the multiple scattering method. By comparing the experimental data with the theoretical findings, the most adequate model for describing the neighbor environment of Fe atoms is chosen. Since the dipole transition matrix element is a smoothly varying function of energy near the Fe K edge, the x-ray absorption fine structure in this energy range characterizes the density of free p states of Fe in the conduction band of Al₉₀Fe_xCe_10?x alloys.     

Optical spectroscopy and electronic structure of compounds HoNi5 − x Al x (x = 0, 1, 2)

The optical properties of the compounds HoNi_{5 ? x} Al _x (x = 0, 1, 2) have been investigated using the ellipsometric method in the wavelength range from 0.22 to 16 μm. The electronic structure of these intermetallic compounds has been calculated in the local electron-spin density approximation with the correction for strong electronic interactions in the 4f shell of the holmium ions. The experimental dispersion dependences of optical conductivity in the region of interband light absorption have been interpreted based on the results of the calculation of the electron density of states. The plasma and relaxation frequencies of electrons have been determined.     

DFT study on size-dependent geometries, stabilities, and electronic properties of AunM2 (M = Si, P; n = 1–8) clusters

The ab initio method based on density functional theory at the PW91PW91 level has been employed to systematically study the structures, stabilities, electronic, and magnetic properties of gold clusters with or without silicon/phosphorus doping. The optimized geometries show that the most stable isomers for Au _n Si₂ and Au _n P₂ (n = 1–8) clusters prefer a three-dimensional structure when n = 2 and n = 3 upwards, respectively, and they can be viewed as grown from the already observed Au _n−1M₂ (M = Si, P). The relative stabilities of calculated Au _n M₂ (M = Si, P) clusters have been analyzed through the atomic average binding energy, fragmentation energy, second-order difference of energy, and HOMO-LUMO gap. A pronounced odd-even alternative phenomenon indicates that the clusters with even-numbered valence electrons possess a higher stability than their neighboring ones. For both systems, natural population analysis reveals that electronic properties of dopant atoms in the corresponding configuration are mainly related to s and p states. We also investigated magnetic effects of clusters as a function of cluster size, however, their oscillatory magnetic moments were found to vary inversely to the fragmentation energy, second-order difference of energy, and HOMO-LUMO gap.     

TDDFT study on electronic excitations and first hyperpolarizabilities of mixed-metal carbonyl clusters MonIr4-n(μ-CO)3(β5-Cp)n (n = 1,2,3)

A series of mixed-metal carbonyl clusters, Mo_nIr_4-n(μ-CO)₃(CO)_9-n(η⁵-Cp)_n (n?=?1, 2; Cp?=?C₅H₄Me, C₅HMe₄, C₅Me₅, C₅H₅), have been investigated using the TDDFT method. The results estimated the medium magnitude of the first static hyperpolarizabilities (β _tot ?～?2?×?10^?30esu) of these tetrahedral mixed-metal clusters, most of which originate from the intra-cluster charge transfer of the metal skeleton consisting of polar metal–metal interactions. No direct contributions of the Cp ligands to the relevant charge transfer were found, but the cooperative effect between the metal centres and Cp ligands impacts the β. Based on these studies a mixed-metal cluster Mo₃Ir(μ-CO)₃(CO)₇(η⁵-Cp)₂ was designed that exhibits enhanced first hyperpolarizability.