CPA treatment of the s-d model at high temperatures

The coherent potential approximation (CPA) is applied to spin-disorder scattering in systems described by the s-d model such as moderately doped magnetic semiconductors. The possibility of a split conduction band at zero temperature is shown to persist also at high temperatures. Band-narrowing is described and conclusions are drawn regarding optical ‘red-shifts’, the Born-approximation, and the paramagnetic spin polaron in narrow energy bands.     

Oscillator strengths and transition probabilities of the Be(I) isoelectronic sequence for 2p2-2s2p and 2s2p-2s2 transitions

Oscillator strengths and transition probabilities are obtained from an intermediate coupling scheme. The initial basis of the eigenstates is formed inLS-coupling. To obtain the resulting energy matrix,Z^-1 perturbation theory is applied. The values of oscillator strengths and transition probabilities for 1s²2p²?1s²2s2p and 1s²2s2p?1s²2s² transitions are calculated and the comparison is made with some recent results. The nuclear charges (Z) involved varied fromZ=4(Be(I)) toZ=35(Br(XXXII)).     

Oscillator strengths for the 2s2, 2p2, 2s3s(1S)-2s2p(1P) transitions of B(II)

Accurate configuration interaction wavefunctions for the 2s²(¹S), 2p²(¹S), 2s3s(¹S) and 2s2p (¹P) states of B(II) are calculated in a single optimized orbital basis of 7s, 6p and 4d Slater-type orbitals. 95, 84, 57 and 90% of the correlation energies, respectively, are realized by these wavefunctions. Oscillator strengths for the three ¹S-¹P transitions are calculated from these and from less accurate wavefunctions in the same orbital basis. The length values obtained from our most accurate wavefunctions, in order of increasing ¹S energy, are 0.9885, 0.202 and 0.007. The degree of accuracy of these oscillator strengths is estimated by noting the convergence to final values as increasing percentages of correlation energies are included in the wavefunctions together with the increasing agreement between length and velocity formulas. The exact theoretical oscillator strength for the resonant line is projected to be 0.985 with an error almost certainly not greater than ±0.015. The theoretical oscillator strengths for the other lines are considered to be 0.21±0.02 and less than 0.007, respectively.     

Relative Cl 2p:P 2s photoionization intensities in transition metal complexes

X-ray photoelectron spectra of the Cl 2p_{$\text{1}\text{2}$, $\text{3}\text{2}$}, P 2s region were obtained for nine transition metal complexes. The Cl:P atom ratios ranged from 1:3 to 3:2 and exhibited a linear relationship with the Cl 2p_{$\text{1}\text{2}$, $\text{3}\text{2}$} : P 2s intensities. Using AlKα radiation, the ratio of the Cl 2p: P 2s photoionization intensities was found to be 2.5: 1.0 with the McPherson ESCA-36 Photoelectron Spectrometer operated in its standard configuration.     

X-ray photoelectron spectra of nickel halides: multiplet structure and multi-electron excitations in Ni2+ 3p and 2p shells

The satellite structure in the X-ray photoelectron spectra of nickel halides has been measured. The satellites found in the photoelectron spectra of Ni²⁺ 3p and 2p subshells have two common sources: multiples splitting and multi-electron excitations. The experimental spectra are compared with theoretical results on multiples splitting and with calculations of band structure.     

P-wave meson production in p + p → d + π+

The total and differential cross sections for the reaction p + p → d + π⁺ are calculated using an initial wave function containing Δ(1236) components generated from the incident protons by means of coupled differential equations. When the width of the Δ is introduced into the differential equations the resonance form of the reaction is obtained. It is found that the ρNΔ coupling can be varied in wide limits without drastic changes in the cross section.     

Single-particle spectrum of a dilute 2D electron gas

Single-particle spectra of a homogeneous 2D electron gas have been calculated in the microscopic functional approach. The effective mass in this system is found to diverge at r _s ? 7. It is shown that the inclusion of the local exchange and correlation corrections to the effective interaction modifies the instability picture from that obtained in the random phase approximation: in the latter, the instability arises away from the Fermi surface, whereas, with the introduction of the corrections, it manifests itself as the divergence of the effective mass.     

Electron energy loss spectra of the silicon 2p, 2s, carbon 1s and valence shells of tetramethylsilane

Inner shell excitation spectra of tetramethylsilane, (CH₃)₄Si, have been measured in the silicon 2s, 2p (L_I,II,III-shell) and carbon is (K-shell) regions using electron energy-loss spectroscopy at an impact energy of 2.5 keV and a scattering angle of ~1°. The high-resolution valence shell spectrum has also been observed at an impact energy of 3 keV and a zero degree scattering angle. The silicon 2p spectra are compared and contrasted with published photoabsorption spectra of SiF₄, SiH₄, and other related Si-containing molecules with varying ligands.     

Linear scaling of the interlayer relaxations of the vicinal Cu(p,p,p − 2) surfaces with the number of atom-rows in the terraces

We investigate the multilayer relaxation trends in the vicinal Cu(p,p,p − 2) surfaces employing the all-electron full-potential linearized augmented plane-wave method. Calculations are performed for the (3 3 1), (2 2 1), (5 5 3), (3 3 2), (7 7 5), and (4 4 3) surfaces, which have 3, 4, 5, 6, 7, and 8 atom-rows in the terrace, respectively. The following trends are identified: (i) The interlayer relaxations perpendicular to the surface scale almost linearly with the number of atom-rows in the terraces. (ii) The nearest-neighbor distances do not depend on the surface termination, but only on the local coordination. (iii) For Cu(p,p,p − 2) in which the topmost n surface layers have nearest-neighbor coordination smaller than the bulk Cu (calculated for the unrelaxed surfaces), the topmost (n − 1) interlayer spacings (d₁₂, … , d_n−1,n) contract compared with the unrelaxed spacing, while the nth interlayer spacing (d_n,n+1) expands. The next (n − 2) interlayer spacings (d_n+1,n+2, … , d_{2n−2,2n−1}) contract, while the interlayer spacing indicated by d_2n−1,2n expands. A similar rule was found for the relaxations parallel to the surfaces. These trends provide a better understanding of the atomic structure of vicinal Cu surfaces.     

Clebsch-Gordan coefficients of the groups SO(p, 1)

An explicit expression for the Clebsch-Gordan coefficients for the coupling of most degenerate unitary representations of SO(p, 1) is obtained.     

A universal covering group of SU(p, q)

A universal covering group of SU(p, q) is parametrized and its groups law in this parametrization is established.     

Z-dependences of atomic characteristics of ions in Be- and O-isoelectronic sequences (2s−2p transition)

Transition energies and probabilities are presented for ions of the Be(Z = 4?100) and O(Z = 8?100) isoelectronic sequences. Dipole transitions are considered between all low-lying states constructed from 2s², 2s2p, and 2p² configuration in the case of Be-like ions, and between all low lying states from 2s²2p⁴, 2s2p⁵, and 2p⁶ configurations in the case of O-like ions. The calculations are based on the $\text{1}\text{Z}$ expansion technique and are carried out in the intermediate coupling scheme. Relativistic effects are incorporated using the Breit operator. For Z > 40, it is shown that jj-coupling is applicable. Results of the present calculations are compared with those of other authors over a broad range of nuclear charges.     

The origin of anomalous temperature dependences of intensities of spin-forbidden d-d transitions in octahedral complexes

It is shown that anomalous temperature dependences of intensities of spin-forbidden d-d transitions, observed in octahedral magnetically-ordering complexes in a paramagnetic phase and in particular in hexagonal RbMnCl₃, investigated by the authors, can be accounted for by a pair-vibrational mechanism, which represents two simultaneous events: breaking of selection rules for spin during pair absorption by exchange coupled ions and breaking of those for parity during an ordinary electronic transition in one of the ions of the pair due to excitation of odd-parity vibrations.     

Observation of the 5pΠu Rydberg state of Li2

Some weak, collisionally induced transitions in ⁷Li₂ have been recorded by Fourier transform spectrometry in the near infrared, following excitation of the 5d¹Π_g state by optical-optical double resonance. They have been assigned as transitions to the 1 ¹Δ_g state from levels v=0 and 1 of a new ungerade Rydberg state, 5p¹Π_u. Quantum defect considerations indicate that the principal quantum number for this new state is 5, and that the assignment to 5p is compatible with a Rydberg series of which the lowest members would be the B¹Π_u and C¹Π_u states.     

Vibrational excitations of p(2×2) oxygen and c(2×2) hydrogen on Pd(100)

The p(2×2) oxygen and c(2×2) hydrogen structures on Pd(100) have been investigated by angle-resolved high-resolution electron energy loss spectroscopy. Dipole excited vibrational modes are observed at 44 and 64 meV for the oxygen and hydrogen structures respectively and are interpreted to correspond to atomic adsorption in the hollow site.     

Dualities and the phase diagram of the p-clock model

A new “bond-algebraic” approach to duality transformations provides a very powerful technique to analyze elementary excitations in the classical two-dimensional XY and p-clock models. By combining duality and Peierls arguments, we establish the existence of non-Abelian symmetries, the phase structure, and transitions of these models, unveil the nature of their topological excitations, and explicitly show that a continuous U(1) symmetry emerges when p?5. This latter symmetry is associated with the appearance of discrete vortices and Berezinskii-Kosterlitz-Thouless-type transitions. We derive a correlation inequality to prove that the intermediate phase, appearing for p?5, is critical (massless) with decaying power-law correlations.     

Invariants of the representations of the group of pseudo-orthogonal matrices,SO(p,q)

The irreducible unitary representations of the group SO(p,q) are investigated by a method based on a study of invariant bilinear functionals. The invariant polylinear functionals are constructed. Integral representations are obtained for the Wigner coefficients and for the crossing symmetrical conformal invariant four-point Green function.     

Single-particle approximation to the canonical density operator of a system of N interacting fermions

A necessary condition for the minimum of free energy Tr(ρH^N) + β^-1 Tr(ρlnρ) is investigated for a system of N interacting fermions on the set of all density matrices of the form ρ=Z^-1 exp(-βNΓ^N₁h¹), where Γ^N₁ is Kummer's (1,N)-expansion map, and h¹ is a finite- dimensional one-particle operator. It is shown that for values of β in an open circle $\text{C}\text{(0,β}{}_0\text{)}$ in the complex plane there exists a unique bounded analytic in β one-particle operator X¹(β) such that Z^-1exp(-βNΓ^N₁X¹(β)) satisfies this condition.     

Direct measurement of the transfer rate pμ+Ar → p+Arμ at high gas pressure

The transfer rate pμ + Ar → p + Arμ has been directly measured in H₂ gas of 600 atm with 2.03 × 10^3̄ at. % Ar at room temperature using delayed coincidence techniques. The transfer rate reduced to an Ar concentration (atoms per unit volume) corresponding to that of liquid hydrogen was found to be (9.8 ± 1.5) × 10¹¹s^?1, which is considerably higher than previous results obtained at lower pressure.     

Structure and vibrations of CO adsorbed on the Ni(100)p(2 × 2)O and c(2 × 2)O surfaces

Chemisorption of CO on the Ni(100)p(2 × 2)O and c(2 × 2)O surfaces has been investigated by high-resolution electron energy loss spectroscopy (EELS) and low-energy electron diffraction (LEED). At 175 K CO adsorption on Ni(100)p(2 × 2)O saturates at about 1 L exposure in a structure interpreted to be Ni(100)p(2 × 2)O—p(2 × 2)CO. The CO layer is stable at 175 K but desorbs readily around 300 K. The EEL spectrum for p(2 × 2)CO shows vibrational losses at 46 meV and 245 meV interpreted to be due to excitations of the Ni-C and C-O stretching vibrations of CO molecules bridge bonded to two nearest neighbour Ni atoms. This interpretation is also supported by the LEED observations. For the preceeding dilute CO layer the vibrational loss spectrum reveals CO adsorption both to Ni bridge sites and hollow sites. At 175 K CO does only adsorb stationary on p(2 × 2)O defects in the Ni(100)c(2 × 2)O surface and not at all on epitaxially grown NiO(111) and (100) surfaces.