Stabilities and interactions of CuRnX and XCuRn (X = F – I): ab initio calculations

Theoretical investigations on the CuRnX and XCuRn (X = F – I) series have been performed at the CCSD(T) theoretical level. Analyses on dissociation energy and frontier orbital show a decreased trend of stabilities down the periodic table. NBO analyses show the existence of σ_Cu-Rn and σ_Cu-X bonding orbital resulted from the overlap between Cu spd hybrid and Rn/X sp hybrid. The Cu–Rn, Cu–X and Rn–X interactions characterised by negative energy density values, positive Laplacian values and small electron densities at bond critical point (BCP) can be described as interactions of moderate strength with partial covalence. Analyses on electron localisation functions, electron density deformations, BCP properties (?G/V and G/ρ) and natural resonance theory demonstrate an increased covalence down the periodic table.     

Pressure-induced structural phase transition and electronic properties of RESb (RE = Ho,Er and Tm) compounds: ab initio calculations

The structural phase transition and electronic properties at ambient (B ₁-phase) and high pressure (B ₂-phase) of heavy rare earth monoantimonides (RESb; RE?=?Ho, Er, and Tm) have been studied theoretically using the self-consistent tight binding linear muffin tin orbital method. These compounds show metallic behavior under ambient condition and undergo a structural phase transition to the B ₂ phase at high pressure. We predict a structural phase transition from the B ₁ to B ₂ phase in the pressure range 30.0–35.0?GPa. Apart from this, the ground state properties, such as lattice parameter and bulk modulus are calculated and compared with the available theoretical and experimental results.     

Tin-stabilized (1 × 2) and (1 × 4) reconstructions on GaAs(100) and InAs(100) studied by scanning tunneling microscopy,photoelectron spectroscopy,and ab initio calculations

Tin (Sn) induced (1 × 2) reconstructions on GaAs(100) and InAs(100) substrates have been studied by low energy electron diffraction (LEED), photoelectron spectroscopy, scanning tunneling microscopy/spectroscopy (STM/STS) and ab initio calculations. The comparison of measured and calculated STM images and surface core-level shifts shows that these surfaces can be well described with the energetically stable building blocks that consist of Sn–III dimers. Furthermore, a new Sn-induced (1 × 4) reconstruction was found. In this reconstruction the occupied dangling bonds are closer to each other than in the more symmetric (1 × 2) reconstruction, and it is shown that the (1 × 4) reconstruction is stabilized as the adatom size increases.     

Feshbach resonances of the C3H− anion: laser autodetachment spectroscopy and ab initio calculations

The electronic spectra of the C₃H^? and C₃D^? anions have been studied above the lowest electron detachment threshold. On the basis of the vibrational, rotational analysis and ab initio calculations, the photodetachment spectrum is assigned to the d³ A″←a³ A″ Feshbach resonance in the bent chain C₃H(D)^? anion. The vibronic system is characterized by a long vibrational progression involving the CCH in plane bending mode ν₄. The potential curves along this coordinate obtained from the spectral analysis and theoretical calculations reveal the importance of vibronic coupling in the electronic excited states. A strong Renner–Teller effect is thought to be the reason for the existence of the Feshbach resonance because the ⁴Σ^? neutral parent and the ³Π anion excited states are close in energy. As for the neutral, ν₄ appears to be the active mode and drives the interaction between the Feshbach and the dipole bound states.     

Nature of M-Ng interaction in the MNg 4 2+ (M = Cu, Ag and Au; Ng = He and Ne) molecules: ab initio calculations

Quantum chemical calculations of the structure and stability of MNg ₄ ²⁺ (M = Cu, Ag and Au; Ng = He and Ne) series at the CCSD(T) theoretical level are performed. The interaction mechanism is investigated using the natural bond orbital (NBO) and electron density analyses. The analyses of the electron density show the weak electrostatic interaction in the system.     

Structural and bonding properties of ScSi_n~-(n=2～6) clusters:photoelectron spectroscopy and density functional calculations

Anion ion photoelectron spectroscopy and density functional theory (DFT) are used to investigate the electronic and structural properties of ScSi_n^- (n=2sim6) clusters and their neutrals. We find that the structures of ScSi_n^- are similar to those of Si_n+1^-. The most stable isomers of ScSi_n^- cluster anions and their neutrals are similar for n=2, 3 and 5 but different for n=4 and 6, indicating that the charge effect on geometry is size dependent for small scandium-silicon clusters. The low electron binding energy (EBE) tails observed in the spectra of ScSi_4,6^- can be explained by the existence of less stable isomers. A comparison between ScSi_n^- and VSi_n^- clusters shows the effects of metal size and electron configuration on cluster geometries.     

Insight into the structural,elastic, electronic,thermoelectric, thermodynamic and optical properties of MRhSb (M = Ti,Zr, Hf) half-Heuslers from ab initio calculations

A detailed theoretical investigation on the structural, elastic, electronic, thermoelectric, thermodynamic and optical properties of half-Heusler MRhSb (M = Ti, Zr, Hf) compounds is presented. The computations are carried out using the full potential linear augmented plane wave method (FP-LAPW) within density functional theory (DFT). The optimized lattice parameters are in fairly good agreement with available experimental data. The computed elastic constants (C_ij) and their related elastic moduli confirm the stability of the studied compounds in the cubic phase and highlight their ductile nature. Analysis of band structures and densities of states (DOS) profiles reveal the semiconducting nature with an indirect energy band gap (Γ-X). The bonding nature discussed via the electron charge density plot shows a mixture of covalent and ionic character. The evaluation of Seebeck coefficient leads to thermopower S ≥ 500 µeV which is very benefic for thermoelectric applications. Estimated thermodynamic characteristic within the quasi-harmonic approximation shows similar behavior for the three compounds. Finally, some optical spectra such as the complex dielectric function, refractive index, reflectivity, energy loss function and absorption are presented.     

Electronic structure of bis(benzo)pentathienoacene in gas and solid phase: ultraviolet photoemission spectroscopy and energy band calculation

Ultraviolet photoemission spectroscopic measurements of bis (benzo)pentathienoacene were carried out in gas and solid phase. For the measurements of solid phase, vacuum deposited films in both amorphous and crystalline phase were prepared on different substrates of HOPG and polycrystalline Au, respectively. The adiabatic ionization energies were determined to be 6.8₄, 5.3₂, and 5.0₈ eV, for gas, amorphous, and crystalline phases, respectively. The spectral lineshapes were interpreted with the aid of the density functional calculations for both isolated molecule and single-crystal structure. The calculated electronic structures were further analyzed in terms of the energy band dispersion and the transport properties of charge carriers.     

Preparation,surface state and band structure studies of SrTi(1 − x)Fe(x)O(3 − δ) (x = 0–1) perovskite-type nano structure by X-ray and ultraviolet photoelectron spectroscopy

In this report, SrTi_(1 ? x)Fe_(x)O_(3 ? δ) photocatalyst powder was synthesized by a high temperature solid state reaction method. The morphology, crystalline structures of obtained samples, was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscopy (TEM), respectively. The electronic properties and local structure of the perovskite STF_x (0 ≤ x ≤ 1) systems have been probed by extended X-ray absorption fine structure (EXAFS) spectroscopy. The effects of iron doping level x (x = 0–1) on the crystal structure and chemical state of the STF_x have been investigated by X-ray photoelectron spectroscopy and the valence band edges for electronic band gaps were obtained for STF_x by ultraviolet photoelectron spectroscopy (UPS). A single cubic perovskite phase of STF_x oxide was successfully obtained at 1200 °C for 24 h by the solid state reaction method. The XPS results showed that the iron present in the STF_x perovskite structure is composed of a mixture of Fe³⁺ and Fe⁴⁺ (SrTi_(1 ? x)[Fe³⁺, Fe⁴⁺]_(x)O_(3 ? δ)). When the content x of iron doping was increased, the amount of Fe³⁺ and Fe⁴⁺ increased significantly and the oxygen lattice decreased on the surface of STF_x oxide. The UPS data has confirmed that with more substitution of iron, the position of the valence band decreased.     

Mechanic,electronic and optical properties of silicides MSi (M = Re,Tc): First-principle calculations

As transition metal silicides have been successfully synthesized, the study of the combination of transition metal and silicon is another effective way to investigate the properties of silicide. We recover novel structures of two silicides: MSi (M?=?Tc, Re). The structures phase are $??FeSi$ phase (P213) and CsCl phase (Pm3m). Using the Cambridge Serial Total Energy Package (CASTEP) code, we researched the mechanical, electronic and optical properties of MSi (M?=?Tc, Re) under 0?GPa and 100?GPa. It is found that each structure is dynamically and mechanically stable at 0?GPa, and the Vickers hardness values show that all of them belong to soft materials. Besides, both the P213-MSi and Pm3m-MSi have metallic characters under 0?GPa and 100?GPa. For the reflectivity in the optical properties, it can be observed that the atom and pressure have obvious influence on the reflectivity of Pm3m-MSi, while only the pressure has obvious influence on the reflectivity of P213-MSi. We hope our work will provide some help to the experimental work on the technologically material.     

Tensor force manifestations in ab initio study of the 2H(d,γ)4He, 2H(d,p)3H, and 2H(d,n)3He reactions

The (2)H(d,p)(3)H, (2)H(d,n)(3)He, and (2)H(d,γ)(4)He reactions are studied at low energies in a multichannel ab initio model that takes into account the distortions of the nuclei. The internal wave functions of these nuclei are given by the stochastic variational method with the AV8' realistic interaction and a phenomenological three-body force included to reproduce the two-body thresholds. The obtained astrophysical S factors are all in very good agreement with the experiment. The most important channels for both transfer and radiative capture are identified by comparing to calculations with an effective central force. They are all found to dominate thanks to the tensor force.     

X-ray photoelectron spectroscopy analysis of (Ln1−xSrx)CoO3−δ (Ln: Pr,Nd and Sm)

The chemical states of the surface of (Ln_0.5Sr_0.5)CoO_3?δ (Ln (lanthanides) = Pr, Nd and Sm) used for cathode materials of intermediate temperature operating solid oxide fuel cells (IT-SOFCs) were investigated by X-ray photoelectron spectroscopy (XPS). Oxygen peaks comprised of lower binding energy (LBE) and higher binding energy (HBE) peaks from (Ln_0.5Sr_0.5)CoO_3?δ and Pr_0.3Sr_0.7CoO_3?δ (PSC37) showed that some merged oxygen peak behavior is a function of the Sr and lanthanide concentrations. By investigating the oxygen peaks, it was determined that more oxygen vacancies were generated on the surface of the cathodes when the lanthanides and Sr were substituted into perovskite oxides. When comparing the binding energies (BEs) of PSC37 with Pr_0.5Sr_0.5CoO_3?δ (PSC55), the LBE and HBE of the Sr peaks both increased when Sr was substituted at the A-site of a perovskite. Surface analysis of the Co peak on the surface of the cathode materials showed that the Co exists mainly as Co³⁺ and partially oxidized to Co⁴⁺ on the cathode materials. The partial existence of Co⁴⁺ can provide some polaron hopping providing electronic conduction for the solid oxide fuel cell.     

Surface electronic structure of single-domain Si( 001) 2 × 2-Al: an angle-resolved photoelectron spectroscopy study using synchrotron radiation

The electronic structure of a single-domain Si(001)2 × 2-Al surface has been studied by angle-resolved photoelectron spectroscopy (ARPES) using synchrotron radiation. Through detailed ARPES measurements along various symmetry axes of the surface Brillouin zone, the existence and dispersions of five surface states are identified, one at binding energies a little less than 1 eV and the others between 1 and 2 eV. The origin of the surface states are discussed in terms of the Al-dimer structures on Si(001).     

Structural,electronic, optical and thermodynamic investigations of NaXF3 (X = Ca and Sr): First-principles calculations

The structural, electronic and optical properties for fluoro-perovskite NaXF₃ (X?=?Ca and Sr) compounds have calculated by WIEN2k code based on full potential linearized augmented plane wave (FP-LAPW) approach within density functional theory (DFT). To perform the total energy calculations, exchange-correlation energy/potential functional has been utilized into generalized gradient approximation (GGA) and local density approximation (LDA). Our evaluated results like equilibrium lattice constants, bulk moduli, and their pressure derivatives are in agreement with the available data. The electronic band structure calculation has revealed an indirect band-gap nature of NaCaF₃, while NaSrF₃ has direct band gap. Total and partial densities of states confirm the degree of localized electrons in different bands. The optical transitions in NaCaF₃ and NaSrF₃ compounds were identified by assigning corresponding peaks obtained from the dispersion relation for the imaginary part of the dielectric function. The thermodynamic properties were calculated using quasi-harmonic Debye model to account lattice vibrations. In addition, the influence of temperature and pressure effects was analyzed on bulk modulus, lattice constant, heat capacities and Debye temperature.     

Electronic structure of La (0001) thin films on W (110) studied by photoemission spectroscopy and first principle calculations

Surface states that have a dz2 symmetry around the center of the surface Brillouin zone(BZ)have been regarded common in closely-packed surfaces of rare-earth metals.In this work,we report the electronic structure of dhcp La(0001)thin films by ultrahigh energy resolution angle-resolved photoemission spectroscopy(ARPES)and first principle calculations.Our first principle analysis is based on the many-body approach,therefore,density function theory(DFT)combined with dynamic mean-field theory(DMFT).The experimentally observed Fermi surface topology and band structure close to the Fermi energy qualitatively agree with first principle calculations when using a renormalization factor of between 2 and 3 for the DFT bands.Photon energy dependent ARPES measurements revealed clear kZ dependence for the hole-like band around the BZ center,previously regarded as a surface state.The obtained ARPES results and theoretical calculations suggest that the major bands of dhcp La(0001)near the Fermi level originate from the bulk La 5d orbits as opposed to originating from the surface states.