683 research outputs found
Hubbard-U calculations for Cu from first-principles Wannier functions
We present first-principles calculations of optimally localized Wannier
functions for Cu and use these for an ab-initio determination of Hubbard
(Coulomb) matrix elements. We use a standard linearized muffin-tin orbital
calculation in the atomic-sphere approximation (LMTO-ASA) to calculate Bloch
functions, and from these determine maximally localized Wannier functions using
a method proposed by Marzari and Vanderbilt. The resulting functions were
highly localized, with greater than 89% of the norm of the function within the
central site for the occupied Wannier states. Two methods for calculating
Coulomb matrix elements from Wannier functions are presented and applied to fcc
Cu. For the unscreened on-site Hubbard for the Cu 3d-bands we have obtained
about 25eV. These results are also compared with results obtained from a
constrained local-density approximation (LDA) calculation.Comment: 13 pages, 8 figures, 5 table
Unscreened Hartree-Fock calculations for metallic Fe, Co, Ni, and Cu from ab-initio Hamiltonians
Unscreened Hartree-Fock approximation (HFA) calculations for metallic Fe, Co,
Ni, and Cu are presented, by using a quantum-chemical approach. We believe that
these are the first HFA results to have been done for crystalline 3d transition
metals. Our approach uses a linearized muffin-tin orbital calculation to
determine Bloch functions for the Hartree one-particle Hamiltonian, and from
these obtains maximally localized Wannier functions, using a method proposed by
Marzari and Vanderbilt. Within this Wannier basis all relevant one-particle and
two-particle Coulomb matrix elements are calculated. The resulting
second-quantized multi-band Hamiltonian with ab-initio parameters is studied
within the simplest many-body approximation, namely the unscreened,
self-consistent HFA, which takes into account exact exchange and is free of
self-interactions. Although the d-bands sit considerably lower within HFA than
within the local (spin) density approximation L(S)DA, the exchange splitting
and magnetic moments for ferromagnetic Fe, Co, and Ni are only slightly larger
in HFA than what is obtained either experimentally or within LSDA. The HFA
total energies are lower than the corresponding LSDA calculations. We believe
that this same approach can be easily extended to include more sophisticated
ab-initio many-body treatments of the electronic structure of solids.Comment: 11 papes, 7 figures, 5 table
Quantum Gravitational Corrections to the Real Klein-Gordon Field in the Presence of a Minimal Length
The (D+1)-dimensional -two-parameter Lorentz-covariant
deformed algebra introduced by Quesne and Tkachuk [C. Quesne and V. M. Tkachuk,
J. Phys. A: Math. Gen. \textbf {39}, 10909 (2006).], leads to a nonzero minimal
uncertainty in position (minimal length). The Klein-Gordon equation in a
(3+1)-dimensional space-time described by Quesne-Tkachuk Lorentz-covariant
deformed algebra is studied in the case where up to first order
over deformation parameter . It is shown that the modified Klein-Gordon
equation which contains fourth-order derivative of the wave function describes
two massive particles with different masses. We have shown that physically
acceptable mass states can only exist for which
leads to an isotropic minimal length in the interval . Finally, we have shown that the above estimation of
minimal length is in good agreement with the results obtained in previous
investigations.Comment: 10 pages, no figur
Self-consistent calculation of total energies of the electron gas using many-body perturbation theory
The performance of many-body perturbation theory for calculating ground-state properties is investigated. We present fully numerical results for the electron gas in three and two dimensions in the framework of the GW approximation. The overall agreement with very accurate Monte Carlo data is excellent, even for those ranges of densities for which the GW approach is often supposed to be unsuitable. The latter seems to be due to the fulfillment of general conservation rules. These results open further prospects for accurate calculations of ground-state properties circumventing the limitations of standard density-functional theory
Magnetic moments of antidecuplet pentaquarks
We analyze the magnetic moment of the exotic pentaquarks of the flavor
antidecuplet in the constituent quark model for the case in which the ground
state is in an orbital L(p)=0(+) or a L(p)=1(-) state. We derive sum rules for
the magnetic moments. The magnetic moment of the Theta(1540) is found to be
0.38, 0.09 and 1.05 mu_N for J(p)=1/2(-), 1/2(+) and 3/2(+), respectively,
which is compared with the results obtained in other approaches.Comment: 15 pages, 1 figure, 3 tables. Revised version, extended introduction
and discussion, accepted for publication in Physics Letters
Response function analysis of excited-state kinetic energy functional constructed by splitting k-space
Over the past decade, fundamentals of time independent density functional
theory for excited state have been established. However, construction of the
corresponding energy functionals for excited states remains a challenging
problem. We have developed a method for constructing functionals for excited
states by splitting k-space according to the occupation of orbitals. In this
paper we first show the accuracy of kinetic energy functional thus obtained. We
then perform a response function analysis of the kinetic energy functional
proposed by us and show why method of splitting the k-space could be the method
of choice for construction of energy functionals for excited states.Comment: 11 page
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
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