1,645 research outputs found
Electron self-energy in A3C60 (A=K, Rb): Effects of t1u plasmon in GW approximation
The electron self-energy of the t1u states in A3C60 (A=K, Rb) is calculated
using the so-called GW approximation. The calculation is performed within a
model which considers the t1u charge carrier plasmon at 0.5 eV and takes into
account scattering of the electrons within the t1u band. A moderate reduction
(35 %) of the t1u band width is obtained.Comment: 4 pages, revtex, 1 figure more information at
http://www.mpi-stuttgart.mpg.de/dokumente/andersen/fullerene
Metal-insulator transitions: Influence of lattice structure, Jahn-Teller effect, and Hund's rule coupling
We study the influence of the lattice structure, the Jahn-Teller effect and
the Hund's rule coupling on a metal-insulator transition in AnC60 (A= K, Rb).
The difference in lattice structure favors A3C60 (fcc) being a metal and A4C60
(bct) being an insulator, and the coupling to Hg Jahn-Teller phonons favors
A4C60 being nonmagnetic. The coupling to Hg (Ag) phonons decreases (increases)
the value Uc of the Coulomb integral at which the metal-insulator transition
occurs. There is an important partial cancellation between the Jahn-Teller
effect and the Hund's rule coupling.Comment: 4 pages, RevTeX, 3 eps figure, additional material available at
http://www.mpi-stuttgart.mpg.de/docs/ANDERSEN/fullerene
Nonlocal density functionals and the linear response of the homogeneous electron gas
The known and usable truly nonlocal functionals for exchange-correlation
energy of the inhomogeneous electron gas are the ADA (average density
approximation) and the WDA (weighted density approximation). ADA, by design,
yields the correct linear response function of the uniform electron gas. WDA is
constructed so that it is exact in the limit of one-electron systems. We derive
an expression for the linear response of the uniform gas in the WDA, and
calculate it for several flavors of WDA. We then compare the results with the
Monte-Carlo data on the exchange-correlation local field correction, and
identify the weak points of conventional WDA in the homogeneous limit. We
suggest how the WDA can be modified to improve the response function. The
resulting approximation is a good one in both opposite limits, and should be
useful for practical nonlocal density functional calculations.Comment: 4 pages, two eps figures embedde
Screening, Coulomb pseudopotential, and superconductivity in alkali-doped Fullerenes
We study the static screening in a Hubbard-like model using quantum Monte
Carlo. We find that the random phase approximation is surprisingly accurate
almost up to the Mott transition. We argue that in alkali-doped Fullerenes the
Coulomb pseudopotential is not very much reduced by retardation
effects. Therefore efficient screening is important in reducing
sufficiently to allow for an electron-phonon driven superconductivity. In this
way the Fullerides differ from the conventional picture, where retardation
effects play a major role in reducing the electron-electron repulsion.Comment: 4 pages RevTeX with 2 eps figures, additional material available at
http://www.mpi-stuttgart.mpg.de/docs/ANDERSEN/fullerene
Iron status in 6-y-old children: associations with growth and earlier iron status
To access publisher full text version of this article. Please click on the hyperlink in Additional Links fieldOBJECTIVE: To investigate the iron status of 6-y-old children and its association with growth and earlier iron status. DESIGN: In a cross-sectional study, children's body size measurements were recorded and blood samples taken near their sixth birthday. SUBJECTS: A sample of 188 children, randomly selected in two previous studies, was contacted, and 139(74%) agreed to participate. RESULTS: No children had iron deficiency anaemia, one was iron-deficient (serum ferritin (SF) or =15 microg/l (258+/-31%; n=49) (P=0.001). MCV at 2 y predicted weight gain from 2 to 6 y (B+/-s.e.=1.721+/-0.581; P=0.005; adj. R2=0.153) (n=44); also, children with SF or =15 microg/l (n=35) gained 9.6+/-2.8 kg (P=0.007), furthermore a difference was seen in proportional weight gain from 2 to 6 y between children with depleted iron stores at 2 y and not, or 156+/-13 vs 169+/-18% (P=0.038). CONCLUSION: The results suggest that low iron status at 1 and 2 y might lead to slower growth up to 6 y of age. Low iron status at 1 and 2 y and/or slower growth from 1 and 2 y up to 6 y might contribute to worse iron status at 6 y, while faster growth in early childhood is related to lower iron status
Optimized Effective Potential Model for the Double Perovskites Sr2-xYxVMoO6 and Sr2-xYxVTcO6
In attempt to explore half-metallic properties of the double perovskites
Sr2-xYxVMoO6 and Sr2-xYxVTcO6, we construct an effective low-energy model,
which describes the behavior of the t2g-states of these compounds. All
parameters of such model are derived rigorously on the basis of
first-principles electronic structure calculations. In order to solve this
model we employ the optimized effective potential method and treat the
correlation interactions in the random phase approximation. Although
correlation interactions considerably reduce the intraatomic exchange splitting
in comparison with the Hartree-Fock method, this splitting still substantially
exceeds the typical values obtained in the local-spin-density approximation
(LSDA), which alters many predictions based on the LSDA. Our main results are
summarized as follows: (i) all ferromagnetic states are expected to be
half-metallic. However, their energies are generally higher than those of the
ferrimagnetic ordering between V- and Mo/Tc-sites (except Sr2VMoO6); (ii) all
ferrimagnetic states are metallic (except fully insulating Y2VTcO6) and no
half-metallic antiferromagnetism has been found; (iii) moreover, many of the
ferrimagnetic structures appear to be unstable with respect to the spin-spiral
alignment. Thus, the true magnetic ground state of the most of these systems is
expected to be more complex. In addition, we discuss several methodological
issues related to the nonuniqueness of the effective potential for the magnetic
half-metallic and insulating states.Comment: 15 pages, 9 figure
Associations of iron status with dietary and other factors in 6-year-old children
To access publisher full text version of this article. Please click on the hyperlink in Additional Links fieldOBJECTIVE: To investigate the associations of iron status at 6 years of age with dietary and other factors. DESIGN: In a cross-sectional study, children's dietary intakes (3-day weighed food record) were recorded, body size was measured and blood samples were taken near their sixth birthday. SUBJECTS: A sample of 188 children, from two previous studies (cohorts 1 and 2), was contacted, and 139 (74%) agreed to participate. RESULTS: Multiple regression analyses with dietary and other factors showed that meat and fish consumption, multivitamin/mineral supplement intake (both positively) and cow's milk product consumption (negatively) were associated with log serum ferritin (SF) (adjusted R (2)=0.125; P=0.028; n=129), and juices and residence (rural>urban) with haemoglobin (Hb) (adjusted R (2)=0.085; P=0.034; n=127). Of 21 multivitamin/mineral consumers, none had depleted iron stores compared to 21 iron-depleted of 108 non-consumers (P=0.024). Children living in rural areas (10,000 inhabitants) (82.1+/-3.2 fl; n=103) (P=0.048). Multiple regression analyses with dietary and other factors and growth showed in cohort 1 that residence (rural>urban), weight gain 0-1years (negatively), and meat and fish intake (positively) were associated with Hb (adjusted R (2)=0.323; P=0.030; n=51), meat and fish (positively) with both log SF (adjusted R (2)=0.069; P=0.035; n=52) and MCV (adjusted R (2)=0.064; P=0.035; n=52), and in cohort 2 cow's milk product consumption (negatively) was associated with log SF (adjusted R (2)=0.119; P=0.017; n=41) and residence (rural>urban) with MCV (adjusted R (2)=0.102; P=0.025; n=41). CONCLUSIONS: Consumption of meat and fish and possibly also juices, as well as multivitamin/mineral intake might affect iron status in 6-year-old children positively, whereas cow's milk product consumption might affect iron status negatively. Slower growth in the first year of life and rural residence are positively related to iron status of 6-year-olds
Arbitrary Choice of Basic Variables in Density Functional Theory. II. Illustrative Applications
Our recent theory (Ref. 1) enables us to choose arbitrary quantities as the
basic variables of the density functional theory. In this paper we apply it to
several cases. In the case where the occupation matrix of localized orbitals is
chosen as a basic variable, we can obtain the single-particle equation which is
equivalent to that of the LDA+U method. The theory also leads to the
Hartree-Fock-Kohn-Sham equation by letting the exchange energy be a basic
variable. Furthermore, if the quantity associated with the density of states
near the Fermi level is chosen as a basic variable, the resulting
single-particle equation includes the additional potential which could mainly
modify the energy-band structures near the Fermi level.Comment: 27 page
Ground State Properties and Optical Conductivity of the Transition Metal Oxide
Combining first-principles calculations with a technique for many-body
problems, we investigate properties of the transition metal oxide from the microscopic point of view. By using the local density
approximation (LDA), the high-energy band structure is obtained, while screened
Coulomb interactions are derived from the constrained LDA and the GW method.
The renormalization of the kinetic energy is determined from the GW method. By
these downfolding procedures, an effective Hamiltonian at low energies is
derived. Applying the path integral renormalization group method to this
Hamiltonian, we obtain ground state properties such as the magnetic and orbital
orders. Obtained results are consistent with experiments within available data.
We find that is close to the metal-insulator transition.
Furthermore, because of the coexistence and competition of ferromagnetic and
antiferromgnetic exchange interactions in this system, an antiferromagnetic and
orbital-ordered state with a nontrivial and large unit cell structure is
predicted in the ground state. The calculated optical conductivity shows
characteristic shoulder structure in agreement with the experimental results.
This suggests an orbital selective reduction of the Mott gap.Comment: 38pages, 22figure
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