1,646 research outputs found
Obtaining Wannier Functions of a Crystalline Insulator within a Hartree-Fock approach: Applications to LiF and LiCl
An ab initio Hartree-Fock approach aimed at directly obtaining the localized
orthogonal orbitals (Wannier functions) of a crystalline insulator is described
in detail. The method is used to perform all-electron calculations on the
ground states of crystalline lithium fluoride and lithium chloride, without the
use of any pseudo or model potentials. Quantities such as total energy, x-ray
structure factors and Compton profiles obtained using the localized
Hartree-Fock orbitals are shown to be in excellent agreement with the
corresponding quantities calculated using the conventional Bloch-orbital based
Hartree-Fock approach. Localization characteristics of these orbitals are also
discussed in detail.Comment: 39 Pages, RevTex, 4 postscript figures, to appear in PRB15, January
9
Wavefunction-based correlated ab initio calculations on crystalline solids
We present a wavefunction-based approach to correlated ab initio calculations
on crystalline insulators of infinite extent. It uses the representation of the
occupied and the unoccupied (virtual) single-particle states of the infinite
solid in terms of Wannier functions. Electron correlation effects are evaluated
by considering virtual excitations from a small region in and around the
reference cell, keeping the electrons of the rest of the infinite crystal
frozen at the Hartree-Fock level. The method is applied to study the ground
state properties of the LiH crystal, and is shown to yield rapidly convergent
results.Comment: 6 pages, RevTex, to appear in Phys. Rev.
Towards a quantum-chemical description of crystalline insulators: A Wannier-function-based Hartree-Fock study of Li2O and Na2O
A recently proposed approach for performing electronic-structure calculations
on crystalline insulators in terms of localized orthogonal orbitals is applied
to the oxides of lithium and sodium, Li2O and Na2O. Cohesive energies, lattice
constants and bulk moduli of the aforementioned systems are determined at the
Hartree-Fock level, and the corresponding values are shown to be in excellent
agreement with the values obtained by a traditional Bloch-orbital-based
Hartree-Fock approach. The present Wannier-function-based approach is expected
to be advantageous in the treatment of electron-correlation effects in an
infinite solid by conventional quantum-chemical methods.Comment: 15 Pages, RevTex, 3 postscript figures (included), to appear in the
Journal of Chemical Physics, May 15, 199
Obtaining correct orbital ground states in electron systems using a nonspherical self-interaction corrected LDA+ method
The electronic structure of lanthanide and actinide compounds is often
characterized by orbital ordering of localized -electrons.
Density-functional theory (DFT) studies of such systems using the currently
available LDA+ method are plagued by significant orbital-dependent
self-interaction, leading to erroneous orbital ground states. An alternative
scheme that modifies the exchange, not Hartree, energy is proposed as a remedy.
We show that our LDA+ approach reproduces the expected degeneracy of
and states in free ions and the correct ground states in solid PrO.
We expect our method to be useful in studying compounds of - and heavy-
elements.Comment: 11 pages, 4 figure
Evaluation of electronic correlation contributions for optical tensors of large systems using the incremental scheme
A new method is developed to calculate the optical tensors of large systems based on available wave function correlation approaches (e.g., the coupled cluster ansatz) in the framework of the incremental scheme. The convergence behaviors of static first- and second-order polarizabilities with respect to the order of the incremental expansion are examined and discussed for the model system Ga4 As4 H18. The many-body increments of optical tensors originate from the dipole-dipole coupling effects and the corresponding contributions to the incremental expansion are compared among local domains with different distances and orientations. The weight factors for increments of optical tensors are found to be tensorial in accordance with the structural symmetry as well as the polarization and the external electric field directions. The long-term goal of the proposed approach is to incorporate the sophisticated molecular correlation methods into the accurate wave function calculation of optical properties of large compounds or even crystals. © 2007 American Institute of Physics.published_or_final_versio
Circular and linear magnetic birefringences in xenon at nm
The circular and linear magnetic birefringences corresponding to the Faraday
and the Cotton-Mouton effects, respectively, have been measured in xenon at
nm. The experimental setup is based on time dependent magnetic
fields and a high finesse Fabry-Perot cavity. Our value of the Faraday effect
is the first measurement at this wavelength. It is compared to theoretical
predictions. Our uncertainty of a few percent yields an agreement at better
than 1 with the computational estimate when relativistic effects are
taken into account. Concerning the Cotton-Mouton effect, our measurement, the
second ever published at nm, agrees at better than
with theoretical predictions. We also compare our error budget with those
established for other experimental published values
Orbital Localization and Delocalization Effects in the U 5f^2 Configuration: Impurity Problem
Anderson models, based on quantum chemical studies of the molecule of
U(C_8H_8)_2, are applied to investigate the problem of an U impurity in a
metal. The special point here is that the U 5f-orbitals are divided into two
subsets: an almost completely localized set and a considerably delocalized one.
Due to the crystal field, both localized and delocalized U 5f-orbitals affect
the low-energy physics. A numerical renormalization group study shows that
every fixed point is characterized by a residual local spin and a phase shift.
The latter changes between 0 and \pi/2, which indicates the competition between
two different fixed points. Such a competition between the different local
spins at the fixed points reflects itself in the impurity magnetic
susceptibility at high temperatures. These different features cannot be
obtained if the special characters of U 5f-orbitals are neglected.Comment: 4 pages, REVTeX, email to [email protected]
Metallic bonding due to correlations: A quantum chemical ab-initio calculation of the cohesive energy of mercury
Solid mercury in the rhombohedral structure is unbound within the
self-consistent field (Hartree-Fock) approximation. The metallic binding is
entirely due to electronic correlations. We determine the cohesive energy of
solid mercury within an ab-initio many-body expansion for the correlation part.
Electronic correlations in the shell contribute about half to the cohesive
energy. Relativistic effects are found to be very important. Very good
agreement with the experimental value is obtained.Comment: 4 pages, 1 figur
The Kondo Box: A Magnetic Impurity in an Ultrasmall Metallic Grain
We study the Kondo effect generated by a single magnetic impurity embedded in
an ultrasmall metallic grain, to be called a ``Kondo box''. We find that the
Kondo resonance is strongly affected when the mean level spacing in the grain
becomes larger than the Kondo temperature, in a way that depends on the parity
of the number of electrons on the grain. We show that the single-electron
tunneling conductance through such a grain features Kondo-induced Fano-type
resonances of measurable size, with an anomalous dependence on temperature and
level spacing.Comment: 4 Latex pages, 4 figures, submitted to Phys. Rev. Let
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