21,260 research outputs found
Strong Coupling Solver for the Quantum Impurity Model
We propose a fast impurity solver for the general quantum impurity model
based on the perturbation theory around the atomic limit, which can be used in
combination with the local density approximation (LDA) and the dynamical mean
field theory (DMFT). We benchmark the solver in the two band Hubbard model
within DMFT against quantum Monte Carlo (QMC) and numerical renormalization
group (NRG) results. We find that the solver works very well in the
paramagnetic Mott insulator phase. We also apply this impurity solver to the
DMFT study of the anti-ferromagnetic phase transition in the unfrustrated Bethe
lattice. The Neel temperature obtained by the fast impurity solver agrees very
well with the QMC results in the large Hubbard U limit. The method is a
promising tool to be used in combination with the LDA+DMFT to study Mott
insulators starting from first principles.Comment: 5 pages, 5 figures. to be published in Physical Review
Casimir Force for Arbitrary Objects Using the Argument Principle and Boundary Element Methods
Recent progress in the simulation of Casimir forces between various objects
has allowed traditional computational electromagnetic solvers to be used to
find Casimir forces in arbitrary three-dimensional objects. The underlying
theory to these approaches requires knowledge and manipulation of quantum field
theory and statistical physics. We present a calculation of the Casimir force
using the method of moments via the argument principle. This simplified
derivation allows greater freedom in the moment matrix where the argument
principle can be used to calculate Casimir forces for arbitrary geometries and
materials with the use of various computational electromagnetic techniques.Comment: 6 pages, 2 figure
Dirac-Kaehler fermion with noncommutative differential forms on a lattice
Noncommutativity between a differential form and a function allows us to
define differential operator satisfying Leibniz's rule on a lattice. We propose
a new associative Clifford product defined on the lattice by introducing the
noncommutative differential forms. We show that this Clifford product naturally
leads to the Dirac-K\"ahler fermion on the lattice.Comment: 3 pages, Lattice2003(Theoretical Development
Simple Recurrent Units for Highly Parallelizable Recurrence
Common recurrent neural architectures scale poorly due to the intrinsic
difficulty in parallelizing their state computations. In this work, we propose
the Simple Recurrent Unit (SRU), a light recurrent unit that balances model
capacity and scalability. SRU is designed to provide expressive recurrence,
enable highly parallelized implementation, and comes with careful
initialization to facilitate training of deep models. We demonstrate the
effectiveness of SRU on multiple NLP tasks. SRU achieves 5--9x speed-up over
cuDNN-optimized LSTM on classification and question answering datasets, and
delivers stronger results than LSTM and convolutional models. We also obtain an
average of 0.7 BLEU improvement over the Transformer model on translation by
incorporating SRU into the architecture.Comment: EMNL
Charge Density Wave Instability and Soft Phonon in PtP (=Ca, Sr, and La)
The electronic and phonon properties of the platinum pnictide superconductors
PtP (=Ca, Sr, and La) were studied using first-principles
calculations. The spin-orbit coupling effect is significant in LaPtP but
negligible in CaPtP and SrPtP, although they all share the same
anti-pevroskite structure. Moreover, SrPtP has been demonstrated to exhibit
an unexpected weak charge-density-wave(CDW) instability which is neither simply
related to the Fermi-surface nesting nor to the momentum-dependent
electron-phonon coupling alone. The instability is absent in CaPtP and can
be quickly suppressed by the external pressure, accompanied with gradual
decreases in the phonon softening and BCS . Our results suggest SrPtP
as a rare example where superconductivity is enhanced by the CDW fluctuations
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