Pair Density Function Research Articles

Short range ordering in amorphous Al 90Fe xCe 10− x

The atomic structure of liquid-quenched amorphous Al 90Fe x Ce 10− x ( x = 5, 7) was studied by diffraction method using X-rays from a synchrotron source. The diffraction data were Fourier-transformed to obtain the atomic pair-density function, and were compared with those obtained by the pulsed neutron scattering to determine the AlFe and AlCe coordination and the extent of compositional short range ordering. The accuracy of the pair-density function, limited by both statistical and systematic errors, is discussed. It was found that both Fe and Ce atoms show strong compositional short range ordering, amounting to 70–80% of the maximum ordering possible. While Ce atoms form a dilute dense random packing substructure, the substructure of Fe atoms and the surrounding Al was found to be substantially different from the random packing.

On the Possibility of Exchange Induced Pairing Mechanism in Model Heavy Fermion Superconducting Systems

AbstractThe periodic Anderson model extended by exchange induced non‐phononic pairing interaction between f‐ and d‐electrons is investigated in the context of singlet like superconductivity. d–d, f–f, and f–d pair density functions are calculated and the stability of different pairing due to various interactions are studied. f–d cross‐over effect is observed and the exchange interaction is found to have the effect of stabilising the pairing; low temperature specific heat is calculated and explained.

Atomic structure of amorphous Al90FexCe10−x

The atomic structure of liquid-quenched amorphous Al90FexCe10−x(x= 5,7) was studied by pulsed neutron and x-ray scattering. The atomic pair-density function determined by pulsed neutron diffraction indicates that a significant portion of Al–Fe distances is anomalously short, while some part of the Al–Al distances is anomalously long. Both neutron and x-ray scattering showed the presence of a prepeak in the structure factor. These results suggest that a strong interaction between A1 and Fe modifies the structure of this glass, leading to chemical and topological short-range ordering.

Inhomogeneous Coulomb fluids with image interactions between planar surfaces. III. Distribution functions

The anisotropic hypernetted chain approximation is used to calculate the one- and two-particle distribution functions for an ionic fluid confined between two charged surfaces. Particular attention is given to the anisotropic distribution functions g(R,R′), c(R,R′), and ρ(R)g(R,R′) (where g, c, and ρ are the pair distribution, direct correlation, and density functions, respectively). They are plotted for various cases and are used to illustrate the mechanisms of the double-layer interaction and other aspects of the system. The effects of image charges (when each surface is a dielectric boundary) and discrete surface charges are investigated.

Role of Microscopic Stress Fluctuations in Glass Transition and Glass Formation

AbstractAlthough the structure of liquids and glasses may appear highly disordered, the atomic motions in these phases are rather strongly correlated. Such a correlation, however, cannot be readily described by a pair density function, and higher order correlation functions are necessary. We suggest that the microscopic stresses defined at each atom are quite useful in describing such high order correlations. We discuss how the concept of the microscopic stress fluctuation helps to describe and understand the glass transition and glass formation phenomena. In a molecular dynamics study the local shear stresses were found to become orientationally correlated below a transition temperature, Ts, which is close to the melting temperature. Below Ts the viscosity shows a rapid increase and transverse phonons become more stable. Thus Ts could be viewed as a dynamical glass transition temperature. The conventional glass transition can be described in terms of the elastic percolation of the orientationally correlated regions. On the other hand, the microscopic stresses in the crystalline solid solutions define the topological stability limit of the crystalline phase, and predict the minimum solute concentration to form stable amorphous alloys.

Molecular electronic distribution functions and correlation holes Theory and application to H2, LiH and BH

The one-electron density functions for the diatomic hydrides H2, LiH and BH, defined with respect to a limited STO basis set, are partially integrated to yield longitudinal and transverse distribution functions which admit of a simple pictorial representation. The maxima in the longitudinal distribution functions occur in regions conventionally ascribed to core pairs, lone pairs or bond pairs. The correlation between pairs of electrons of given spin is then analysed in terms of the analogous partially integrated pair density functions and in terms of the associated hole functions. In the case of LiH and BH, the Fermi hole functions are similar in form to the negatives of the one-electron distribution functions for the appropriate singly occupied molecular orbitals; but the differences between the two functions are more marked in BH, where there is increased spatial interpenetration of the valence electron pairs. The results also show, in a simple way, how the electron motion is over-correlated in H2 when ...

Nonuniform states of an imperfect bose gas

The low-lying states of an inhomogeneous weakly interacting Bose gas are investigated with the Bogoliubov transformation. The particle density n(r), the particle current j(r), and the pair density function n 2(r, r′) are evaluated at finite temperature T, including both condensate and noncondensate contributions. For a uniformly moving condensate, j is proportional to the Landau superfluid density ϱ s ( T). For a singly quantized vortex with core radius ξ, the asymptotic properties ( r → ∞) are given by n( r) ∼ n [1 + O( ξ 2 r 2 )] and j θ(r) ∼ ( n h ̵ mr )[1 + O( ξ 2 r 2 )] , where n = n 0 + n′ is the total density (condensate plus noncondensate) in a uniform system. Near the axis of the vortex, n(0) = n′(0) is estimated to be ≈ 1.4 n′, yet j θ ( r) vanishes linearly, implying a finite kinetic energy density in the core. The N-body wave function in configuration space is constructed for the lowest state of a vortex. It suggests an improved form of the trial function used by Chester, Metz, and Reatto for a vortex in 4He.