Ab initio calculations for properties of MAX phases Ti2InC,Zr2InC,and Hf2InC

We have computed the lattice constants, bulk modulus, and total- and partial-density of states of MAX phases Ti₂InC, Zr₂InC and Hf₂InC in the hexagonal P6₃/mmc space group by ab initio calculation. The deviations from the experimental values for lattice constants are below 1.6%. The bulk moduli are computed to be 128 GPa, 113 GPa, and 136 GPa, respectively. The Zr₂InC has the lowest bulk modulus among all MAX phases studied to date, which is related to the weaker covalent interaction between Zr-d and C-s, C-p states.     

Detection and study of Rb I Rydberg states

We describe the details of an experiment using an atomic beam of rubidium which allowed us to detect by field ionization techniques the np Rydberg states from n = 28 up to n = 78, to detect also ns and nd states using a Stark mixing, and for all of these detected states to check the classical law E_c = [16n^*4]^?1 concerning the critical ionizing electric field E_c. It turns out that for n as high as 65 this law is quite well verified.     

Study on the electronic structures of the reduced anatase TiO2 by the first-principle calculation

Employing the first-principle calculations based on the density functional theory (DFT) and the Molecule Orbital theory (MO), we have researched the electronic structures of the reduced anatase TiO₂ and its visible light photoactivity. The study is emphasized on the O vacancy, including the components of the defect states, the relationship with the bulk states and the way in which these electrons occupying the defect states are distributed in the real space. We find that the origin of the visible light photoactivity should be due to the transition of the excited electrons from the defect states σ_g orbital to the σ_u orbital in the upper conduction bands, rather than arising from the reduction of the band gap. The calculated results indicate that the localized defect states induced by the neutral and doubly ionized oxygen vacancies are all located in the band gap.     

Hydrogen-induced states in VHx and VDx observed by soft X-ray emission spectroscopy

From measurements of soft X-ray emission spectra (V-L₃) of VH_x and VD_x, a gradual change of d-band of V metal with addition of H(D), and an appearance of H(D)-induced states immediately below the d-band, are clearly demonstrated. The states, located at 7 eV below the Fermi energy for all compositions, are interpreted as being bonding states formed by H(D)-1s and V-3d orbitals. No isotope effects were detected within the accuracy of the experiment.     

First-principles study of ferromagnetism in N doped TiO2 and TiO

N doped TiO is nonmagnetic, in which spin-split impurity states are not induced near the Fermi energy (E_F) by N dopant. N doped TiO₂ along with transition-metal (TM) doped TiO is magnetic, in which spin-split impurity states are induced across E_F. The magnetic moment is determined by the 3d4s electron configurations and the valence states of TM-dopant ions when they substitute Ti. Hence, the origin of ferromagnetism of N doped TiO₂ and TiO is not closely related to the width of the band gaps of host oxides, but would be crucially related to that if the dopant can induce spin-split impurity states near E_F.     

The effective Hamiltonian for the coupling between inversion-torsion states in methylamine

The Hougen’s formalism of group-theoretical effective Hamiltonian has been extended to include the resonances between the wagging, ν₉, and third or fourth excited torsional, 3ν₁₅ and 4ν₁₅, states in methylamine. The presented Hamiltonian treats explicitly these couplings. For each of these bands the rovibrational sublevels belong to all symmetry species of the G₁₂ group of methylamine. On the other hand the vibrational states for ν₉ and 4ν₁₅ are symmetric with respect to reflection in the symmetry plane of the NH₂ group, and antisymmetric for 3ν₁₅. We have shown that the coupling terms between the ν₉ and 3ν₁₅ states are limited to Coriolis-like coupling, and no Fermi-type interactions are allowed. For the coupling between the ν₉ and 4ν₁₅ states all kind of interaction terms are possible.     

Spectroscopic properties of SbH

Relativistic configuration interaction calculations which include spin-orbit interaction are carried out for nine low-lying ω-ω states and four λ-s states. Spectroscopic properties of six bound ω-ω states are reported. These calculations not only enable assignment of the experimentally observed X₁, X₂, A₁, A₂, and B states but also predict the properties of other electronic states (0⁺(II), 0⁺(IV), 2, 2(II), 1(II), 0⁻) which are yet to be observed. The dissociation energy of SbH is predicted to be 2.7 ± 0.2 eV.     

Vibration-rotation energies of harmonic and combination levels in tetrahedral XY4 molecules: Theory and extrapolation method

This paper presents a general method for studying overtones and combination bands of tetrahedral XY₄ molecules. Making full use of group theory, the matrix representation of the Hamiltonian restricted to any set of vibrational sublevels is easily derived from a basis of rovibrational matrices. Explicit expressions for the reduced matrix elements are developed for all the operators of any order occurring in states for which Σ_sv_s ≤ 2, including any interaction type. The parameters introduced are directly the Hamiltonian expansion coefficients and consequently have the same physical significance in any vibrational state. The treatment of overtones and combination bands for which the corresponding fundamentals are analyzed is considered in detail. In this case, the parameters of the ground and fundamental states remain fixed and only a few new parameters occurring specifically in the studied state need to be determined. In this way, the convergence of least-squares fits is greatly improved. The example of methane is used to illustrate the efficiency of this method suitable for the direct determination of potential constants.     

Stretching vibrational overtone and combination states in silicon tetrafluoride

A simple three-parameter model is shown to account for the observed SiF stretching vibrational states of silicon tetrafluoride. A symmetrized anharmonic bond oscillator basis set is used to calculate stretching overtone and combination eigen values, all of which are given up to v₁ + v₃ = 5. The results show that the highest levels of the nν₃ manifold move gradually out of resonances with n quanta of ν₃ as n increases, which indicates that anharmonic resonances between the ν₃ ladder and some other vibrational ladders and (or) multiphoton resonances are needed to explain the observed multiphoton processes.     

Electronic structures and magnetic properties of CrSiTe3 single-layer nanoribbons

One-dimensional nanoribbons usually exhibit considerably different properties compared to their monolayer counterparts due to the formation of edge states and limited width. In this study, we systematically investigate the stability, electronic structures and magnetic properties of CrSiTe₃ single-layer nanoribbons with different edge configurations and ribbon widths using first-principles calculations. The results show that the edge energies (less than 0.4 eV/Å) for all studied CrSiTe₃ nanoribbons are much lower than that of graphene and many transition-metal dichalcogenide nanoribbons, indicating their stability and easy formation. Compared to the CrSiTe₃ monolayer with ferromagnetic semiconductor characteristics, some of CrSiTe₃ nanoribbons (N-SiCr-ZNRs, N-Te-ZNRs, N-TeCr-ANRs and N-Te-ANRs) become half-metal due to the hybridization between the d orbitals of edge Cr atoms and the p orbitals of edge Te atoms. While N-SiTe-ANRs are bipolar magnetic semiconductors, in which the states near Fermi level are localized around the nanoribbons edge. Our results show that CrSiTe₃ single-layer nanoribbons are promising candidates suitable for applications in spintronic devices.     

Ion-pair states of I<Subscript>2</Subscript>, Br<Subscript>2</Subscript>, IBr,and ICl

The experimentally determined energies and rotational constants of the vibrational levels v = 0–20 of the Ion-Pair states Ω = 0⁺, Ω = 1 of the I₂, Br₂, IBr, and ICl molecules are modeled. The model used includes three diabatic states, which correlate to X⁺(3P, 1D) + Y^～(1S₀). These states are coupled by the spin-orbit interaction, which is assumed to be independent of the internuclear distance. For IBr and ICl, as well as for the ungerade states of I₂ and Br₂, satisfactory results are obtained. The model is less applicable to the gerade states of I₂ and Br₂, which is possibly results from the retainment of the asymptotic J _A J _B coupling of the angular momenta at equilibrium internuclear distances.     

Weitere Messungen zur Anisotropie der intermolekularen Wechselwirkung durch Streuung von Molekülen in definiertem Quantenzustand

Improved measurements of the ratio of scattering cross sections for various molecular rotational states are reported for scattering of TlF in rotational states ¦J, M〉=¦1, 0〉 and ¦1, 1〉, and CsF in rotational states ¦2, 0〉 and ¦2, 2〉 by rare gases. The results are interpreted in terms of an angle dependent attractive potentialV=?2ε(r _m /r) ⁶(1+q ₆ P ₂(cosΘ) in which the repulsive part of the interaction is neglected. The “high energy” approximation is used to calculate the cross section, which contains the velocity dependence and the state dependence as factors. The experiments show for all scattering partners with the exception of He and Ne, that the state dependence is velocity independent. In those cases this result provides a justification for the neglect of the repulsive potential term. The results for the anisotropy parameterq ₆, which to a good approximation depends only on properties of the moleculus, are:q ₆=0.23±0.01 for TlF,q ₆=0.28±0.02 for CsF.     

The Goldberger-Treiman relation and the chiral soliton model

The linear chiral soliton model with explicit quark fields and elementary pion- and sigma-fields is solved in order to describes nucleon and delta properties. Special emphasis is put on the axial vector coupling constant g_A and on the Goldberger-Treiman relation. To this end baryon Fock states are constructed in a mean field approximation with hedgehog-like configurations from which the physical states are obtained by projection techniques. It is shown that the Goldberger-Treiman relation is only fulfilled if the quark- and pion-hedgehog is generalized and the variation is performed with projected states. Under this condition no parameter set is found which yields a proper g_A and a proper pion-nucleon coupling constant g_πNN, if the polarization of the Dirac sea is neglected. Other observables are reproduced within 20% limits or less.     

Europium silicides and germanides of the EuM2X2 type: Crystal structure and the valence states of europium

X-ray diffraction studies of EuM₂X₂ compounds (M = Fe, Co, Ni, Cu; X = Si, Ge) revealed that these compounds crystallize in the ThCr₂Si₂ type body-centered tetragonal structure, with the space group $\text{I4}\text{mmm}$. Distribution of the atoms among the lattice sites, the free parameter of the Si and Ge atoms, and the interatomic distances of the compounds were determined by crystal structure calculations. Europium, as determined by Mössbauer spectroscopy, is present in the di- and tri-valent states in the EuM₂Si₂ compounds, the relative amounts of the two states being different in each of the compounds. In EuNiSi₃, EuNi₂Ge₂ and EuCu₂Ge₂ all the Eu are divalent. The relationship between the structure properties and the valence states of Eu in the compounds is discussed.     

QCD sum rules for heavy quark systems

In this paper we present in a detailed and coherent fashion our work on QCD sum rules for equal mass heavy quark meson states. We discuss the technical procedures used to calculate the perturbative and non-perturbative contributions to the vacuum polarization, which have been calculated for all currents up to and including spin 2⁺⁺. Using dispersion relations, sum rules are derived. Extensive applications are made to the lowest lying states of the charmonium and upsilon systems. The masses of the S- and P-wave charmonium levels are reproduced to a high degree of accuracy, and the mass of the ¹P₁ level is predicted at 3.51 GeV. For the upsilon system it only appears to be possible to predict the γ-η_b splitting which gives 60 MeV. Very accurate values are given for the current quark masses at p² = ?m_q²: m_c = 1.28 GeV and m_b = 4.25 GeV.     

On the emergence of superconductivity and hysteresis in a cylindrical type I superconductor

One-dimensional vortex-free solutions of the system of Ginzburg-Landau equations (the so-called precursor states) are studied. These states describe the emergence of superconductivity in a long cylindrical type I superconductor, which was initially in the supercooled normal state in a magnetic field, and are formed upon subsequent reduction of the external field. The precursor states are responsible for the magnetic hysteresis in type I superconductors (for which κ < κ_c, where κ_c (R) is the critical value of the parameter κ in the Ginzburg-Landau theory, which is a function of radius). The range of fields is determined in which precursor states exist along with the Meissner state (and a hysteresis is possible) in the dependence of the cylinder radius R and parameter κ.     

Coexistence of the superconducting condensate and the quasi-stationary states of hole pairs

The formation of bound states in the case of a direct Coulomb repulsion between two holes whose reciprocal effective mass tensor has principal values of opposite signs is considered as a possible mechanism of high-T _C superconductivity. The study of the specific features of the scattering amplitude shows that, under certain conditions, in addition to the quasi-stationary states, states with a negative attenuation are possible, which corresponds to the tendency toward the formation of a hole pair condensate. The coexistence of the quasi-stationary states and the condensate qualitatively agrees with the phase diagram of p-type doped high-T _C superconducting cuprates.     

Rydberg states of carbon dioxide and carbon disulfide

The electronic absorption spectra of carbon dioxide and carbon disulfide have been reexamined. Model potential calculations have been used to calculate the energies of excited states in Rydberg approximation, and (npσ) and (npπ) Rydberg series have been assigned. For both molecules, the lowest excited ¹Π_g and ¹Π_u states are identified as Rydberg states. The lowest ${}^1\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}$ state is mainly Rydberg for CO₂, but contains some valence character for CS₂, There is no evidence for transitions to additional valence states of these symmetries.It is shown that $\text{LCAO}\text{MO}$ predictions about excited states can be misleading because of near-linear dependencies which arise in multicenter expansions. A consideration of the united atom orbitals for CO₂ and CS₂ predicts that there should be only the number of low-energy excited states which are found from the spectral analysis.