890 research outputs found
Optimizing momentum space DMRG using quantum information entropy
In order to optimize the ordering of the lattice sites in the momentum space
and quantum chemistry versions of the density matrix renormalization group
(DMRG) method we have studied the separability and entanglement of the target
state for the 1-D Hubbard model and various molecules. By analyzing the
behavior of von Neumann and Neumann-Renyi entropies we have found criteria that
help to fasten convergence. A new initialization procedure has been developed
which maximizes the Kullback-Leibler entropy and extends the active space (AS)
in a dynamical fashion. The dynamically extended active space (DEAS) procedure
reduces significantly the effective system size during the first half sweep and
accelerates the speed of convergence of momentum space DMRG and quantum
chemistry DMRG to a great extent. The effect of lattice site ordering on the
number of block states to be kept during the RG procedure is also investigated.Comment: 15 pages, 15 figure
Scaling and Decoherence in the Out-of-Equilibrium Kondo Model
We study the Kondo effect in quantum dots in an out-of-equilibrium state due
to an applied dc-voltage bias. Using the method of infinitesimal unitary
transformations (flow equations), we develop a perturbative scaling picture
that naturally contains both equilibrium coherent and non-equilibrium
decoherence effects. This framework allows one to study the competition between
Kondo effect and current-induced decoherence, and it establishes a large regime
dominated by single-channel Kondo physics for asymmetrically coupled quantum
dots.Comment: 4 pages, 3 figures; v2: minor changes (typos corrected, esp. in Eqs.
(3), (4), references updated, improved layout for figures
Unified phase diagram of models exhibiting neutral-ionic transition
We have studied the neutral-ionic transition in organic mixed-stack
compounds. A unified model has been derived which, in limiting cases, is
equivalent to the models proposed earlier, the donor-acceptor model and the
ionic Hubbard model. Detailed numerical calculations have been performed on
this unified model with the help of the density-matrix renormalization-group
(DMRG) procedure calculating excitation gaps, ionicity, lattice site entropy,
two-site entropy, and the dimer order parameter on long chains and the unified
phase diagram has been determined.Comment: 11 pages, 8 figure
Szépirodalmi szövegek nyelvi és stilisztikai vizsgálata a magyart mint idegen nyelvként tanuló diákokkal
Stílus és fogalmi integráció főnév→melléknév szófajváltással keletkezett magyar neologizmusokban
The coexistence of Swabians and Hungarians in a village in near Budapest
The study takes the contact hypothesis of social psychology as its starting point and examines a Swabian-Hungarian ethnic village as an example.The contact hypothesis suggests that contact or interaction between members of different groups under the right circumstances diminishes prejudice and hostility between those groups and mitigates stereotyping and discrimination. However, for this effect to occur, certain conditions
must be met: the parties should be of equal status, have a common goal, cooperate, receive the support of authorities and maintain a personal relationship, since this is the only way long-
term success can be achieved. Pursuit of mutual assimilation, physical proximity and time can also help people to accept each other and adopt coexistence. These conditions have been met in the case of the Swabian and Hungarian ethnic groups living in the village of Dunabogdány. Social and political processes, Catholicism and the fact that the German language has been added to the local school curriculum have also contributed to the successful outcome
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