146 research outputs found
The calculation method of interaction between metal atoms under influence of the radiation
A method of calculation of interatomic interaction potentials in the presence of ionized states has been developed. They have been obtained for the atoms with different ionization degree on example of aluminum. The Heine-Abarenkov-Animalu model potential form factors was employed. The form factor parameters of ionized atoms was determined on the base of the quantum defect method using the atomic-spectroscopy data. The potential of interatomic interaction for different charged states with different degree of ionization were determined
High-speed grating interferometry
We present the most recent advances in fast X-ray grating interferometer and their applications. A dedicated setup for rapid scanning with a single grating and using filtered broadband illumination of an undulator source has been implemented. With this setup, grating interferometer tomographic scans can be achieved within few minutes owing to the filtered broadband beam and single-grating spatial harmonic imaging technique. Use of this system on the chemical processes happening in few millisecond time span is presented. This beam condition is very stable which is very difficult to achieve with the monochromatic beams. Tomographic phase volume rendering obtained with this beam condition is explained. We will also describe the new capabilities and applications
Pair distribution function in a two-dimensional electron gas
We calculate the pair distribution function, , in a two-dimensional
electron gas and derive a simple analytical expression for its value at the
origin as a function of . Our approach is based on solving the
Schr\"{o}dinger equation for the two-electron wave function in an appropriate
effective potential, leading to results that are in good agreement with Quantum
Monte Carlo data and with the most recent numerical calculations of . [C.
Bulutay and B. Tanatar, Phys. Rev. B {\bf 65}, 195116 (2002)] We also show that
the spin-up spin-down correlation function at the origin, , is mainly independent of the degree of spin polarization of
the electronic system.Comment: 5 figures, pair distribution dependence with distance is calculate
A Geometric Formulation of Quantum Stress Fields
We present a derivation of the stress field for an interacting quantum system
within the framework of local density functional theory. The formulation is
geometric in nature and exploits the relationship between the strain tensor
field and Riemannian metric tensor field. Within this formulation, we
demonstrate that the stress field is unique up to a single ambiguous parameter.
The ambiguity is due to the non-unique dependence of the kinetic energy on the
metric tensor. To illustrate this formalism, we compute the pressure field for
two phases of solid molecular hydrogen. Furthermore, we demonstrate that
qualitative results obtained by interpreting the hydrogen pressure field are
not influenced by the presence of the kinetic ambiguity.Comment: 22 pages, 2 figures. Submitted to Physical Review B. This paper
supersedes cond-mat/000627
Electronic resonance states in metallic nanowires during the breaking process simulated with the ultimate jellium model
We investigate the elongation and breaking process of metallic nanowires
using the ultimate jellium model in self-consistent density-functional
calculations of the electron structure. In this model the positive background
charge deforms to follow the electron density and the energy minimization
determines the shape of the system. However, we restrict the shape of the wires
by assuming rotational invariance about the wire axis. First we study the
stability of infinite wires and show that the quantum mechanical
shell-structure stabilizes the uniform cylindrical geometry at given magic
radii. Next, we focus on finite nanowires supported by leads modeled by
freezing the shape of a uniform wire outside the constriction volume. We
calculate the conductance during the elongation process using the adiabatic
approximation and the WKB transmission formula. We also observe the correlated
oscillations of the elongation force. In different stages of the elongation
process two kinds of electronic structures appear: one with extended states
throughout the wire and one with an atom-cluster like unit in the constriction
and with well localized states. We discuss the origin of these structures.Comment: 11 pages, 8 figure
Self-consistent Overhauser model for the pair distribution function of an electron gas in dimensionalities D=3 and D=2
We present self-consistent calculations of the spin-averaged pair
distribution function for a homogeneous electron gas in the paramagnetic
state in both three and two dimensions, based on an extension of a model that
was originally proposed by A. W. Overhauser [Can. J. Phys. {\bf 73}, 683
(1995)] and further evaluated by P. Gori-Giorgi and J. P. Perdew [Phys. Rev. B
{\bf 64}, 155102 (2001)]. The model involves the solution of a two-electron
scattering problem via an effective Coulombic potential, that we determine
within a self-consistent Hartree approximation. We find numerical results for
that are in excellent agreement with Quantum Monte Carlo data at low and
intermediate coupling strength , extending up to in
dimensionality D=3. However, the Hartree approximation does not properly
account for the emergence of a first-neighbor peak at stronger coupling, such
as at in D=2, and has limited accuracy in regard to the spin-resolved
components and . We also
report calculations of the electron-electron s-wave scattering length, to test
an analytical expression proposed by Overhauser in D=3 and to present new
results in D=2 at moderate coupling strength. Finally, we indicate how this
approach can be extended to evaluate the pair distribution functions in
inhomogeneous electron systems and hence to obtain improved
exchange-correlation energy functionals.Comment: 14 pages, 7 figuers, to apear in Physical Review
Hellmann-Feynman theorem and fluctuation-correlation analysis of the Calogero-Sutherland model
Exploiting the results of the exact solution for the ground state of the
one-dimensional spinless quantum gas of Fermions and impenetrable Bosons with
the mu/x_{ij}^2 particle-particle interaction, the Hellmann-Feynman theorem
yields mutually compensating divergences of both the kinetic and the
interaction energy in the limiting case mu to -1/4. These divergences result
from the peculiar behavior of both the momentum distribution (for large
momenta) and the pair density (for small inter-particle separation). The
available analytical pair densities for mu=-1/4, 0, and 2 allow to analyze
particle-number fluctuations. They are suppressed by repulsive interaction
(mu>0), enhanced by attraction (mu<0), and may therefore measure the kind and
strength of correlation. Other recently proposed purely quantum-kinematical
measures of the correlation strength arise from the small-separation behavior
of the pair density or - for Fermions - from the non-idempotency of the
momentum distribution and its large-momenta behavior. They are compared with
each other and with reference-free, short-range correlation-measuring ratios of
the kinetic and potential energies.Comment: 30 pages, 9 figures, revised version, short version appeared as PRB
62, 15279-15282 (2000
Extended Hartree-Fock method based on pair density functional theory
A practical electronic structure method in which a two-body functional is the
fundamental variable is constructed. The basic formalism of our method is
equivalent to Hartree-Fock density matrix functional theory [M. Levy in {\it
Density Matrices and Density Functionals}, Ed. R. Erdahl and V. H. Smith Jr.,
D. Reidel, (1987)]. The implementation of the method consists of solving
Hartree-Fock equations and using the resulting orbitals to calculate two-body
corrections to account for correlation. The correction terms are constructed so
that the energy of the system in the absence of external potentials can be made
to correspond to approximate expressions for the energy of the homogeneous
electron gas. In this work the approximate expressions we use are based on the
high-density limit of the homogeneous electron gas. Self-interaction is
excluded from the two-body functional itself. It is shown that our pair density
based functional does not suffer from the divergence present in many density
functionals when homogeneous scaling is applied. Calculations based on our pair
density functional lead to quantitative results for the correlation energies of
atomic test cases.Comment: to appear in Physical Review
Density-functional theory of elastically deformed finite metallic system: work function and surface stress
The effect of external strain on surface properties of simple metals is
considered within the modified stabilized jellium model. The equations for the
stabilization energy of the deformed Wigner-Seitz cells are derived as a
function of the bulk electron density and the given deformation. The results
for surface stress and work function of aluminium calculated within the
self-consistent Kohn-Sham method are also given. The problem of anisotropy of
the work function of finite system is discussed. A clear explanation of
independent experiments on stress-induced contact potential difference at metal
surfaces is presented.Comment: 15 pages, 1 figur
Electronic Structure Calculation by First Principles for Strongly Correlated Electron Systems
Recent trends of ab initio studies and progress in methodologies for
electronic structure calculations of strongly correlated electron systems are
discussed. The interest for developing efficient methods is motivated by recent
discoveries and characterizations of strongly correlated electron materials and
by requirements for understanding mechanisms of intriguing phenomena beyond a
single-particle picture. A three-stage scheme is developed as renormalized
multi-scale solvers (RMS) utilizing the hierarchical electronic structure in
the energy space. It provides us with an ab initio downfolding of the global
band structure into low-energy effective models followed by low-energy solvers
for the models. The RMS method is illustrated with examples of several
materials. In particular, we overview cases such as dynamics of semiconductors,
transition metals and its compounds including iron-based superconductors and
perovskite oxides, as well as organic conductors of kappa-ET type.Comment: 44 pages including 38 figures, to appear in J. Phys. Soc. Jpn. as an
invited review pape
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