1,757 research outputs found
A novel FLEX supplemented QMC approach to the Hubbard model
This paper introduces a novel ansatz-based technique for solution of the
Hubbard model over two length scales. Short range correlations are treated
exactly using a dynamical cluster approximation QMC simulation, while
longer-length-scale physics requiring larger cluster sizes is incorporated
through the introduction of the fluctuation exchange (FLEX) approximation. The
properties of the resulting hybrid scheme are examined, and the description of
local moment formation is compared to exact results in 1D. The effects of
electron-electron coupling and electron doping on the shape of the
Fermi-surface are demonstrated in 2D. Causality is examined in both 1D and 2D.
We find that the scheme is successful if QMC clusters of are used
(with sufficiently high temperatures in 1D), however very small QMC clusters of
lead to acausal results
A Non-Crossing Approximation for the Study of Intersite Correlations
We develop a Non-Crossing Approximation (NCA) for the effective cluster
problem of the recently developed Dynamical Cluster Approximation (DCA). The
DCA technique includes short-ranged correlations by mapping the lattice problem
onto a self-consistently embedded periodic cluster of size . It is a fully
causal and systematic approximation to the full lattice problem, with
corrections in two dimensions. The NCA we develop is a
systematic approximation with corrections . The method will
be discussed in detail and results for the one-particle properties of the
Hubbard model are shown. Near half filling, the spectra display pronounced
features including a pseudogap and non-Fermi-liquid behavior due to
short-ranged antiferromagnetic correlations.Comment: 12 pages, 11 figures, EPJB styl
Spectral Properties and Bandstructure of Correlated Electron Systems
We present -dependent one-particle spectra and corresponding
effective bandstructures for the Hubbard model calculated within the
dynamical molecular field theory (DMFT). This method has proven to yield highly
nontrivial results for a variety of quantities but the question remains open to
what extent it is applicable to relevant physical situations.
To address this problem we compare our results for spectral functions to
those obtained by QMC simulations. The good agreement supports our notion that
the DMFT is indeed a sensible ansatz for correlated models even in to .Comment: Paper presented at SCES '95, Sept. 27 - 30 1995, Goa. To be published
in Physica B. 10 pages, figures include
Transport Properties of the Infinite Dimensional Hubbard Model
Results for the optical conductivity and resistivity of the Hubbard model in
infinite spatial dimensions are presented. At half filling we observe a gradual
crossover from a normal Fermi-liquid with a Drude peak at in the
optical conductivity to an insulator as a function of for temperatures
above the antiferromagnetic phase transition. When doped, the ``insulator''
becomes a Fermi-liquid with a corresponding temperature dependence of the
optical conductivity and resistivity. We find a -coefficient in the low
temperature resistivity which suggests that the carriers in the system acquire
a considerable mass-enhancement due to the strong local correlations. At high
temperatures, a crossover into a semi-metallic regime takes place.Comment: 14 page
First principle electronic, structural, elastic, and optical properties of strontium titanate
We report self-consistent ab-initio electronic, structural, elastic, and
optical properties of cubic SrTiO perovskite. Our non-relativistic
calculations employed a generalized gradient approximation (GGA) potential and
the linear combination of atomic orbitals (LCAO) formalism. The distinctive
feature of our computations stem from solving self-consistently the system of
equations describing the GGA, using the Bagayoko-Zhao-Williams (BZW) method.
Our results are in agreement with experimental ones where the later are
available. In particular, our theoretical, indirect band gap of 3.24 eV, at the
experimental lattice constant of 3.91 \AA{}, is in excellent agreement with
experiment. Our predicted, equilibrium lattice constant is 3.92 \AA{}, with a
corresponding indirect band gap of 3.21 eV and bulk modulus of 183 GPa.Comment: 11 pages, 6 figures,Accepted for publication in AIP Advances (2012
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