1,226 research outputs found
Status and Future Perspectives for Lattice Gauge Theory Calculations to the Exascale and Beyond
In this and a set of companion whitepapers, the USQCD Collaboration lays out
a program of science and computing for lattice gauge theory. These whitepapers
describe how calculation using lattice QCD (and other gauge theories) can aid
the interpretation of ongoing and upcoming experiments in particle and nuclear
physics, as well as inspire new ones.Comment: 44 pages. 1 of USQCD whitepapers
Simulating the weak death of the neutron in a femtoscale universe with near-Exascale computing
The fundamental particle theory called Quantum Chromodynamics (QCD) dictates
everything about protons and neutrons, from their intrinsic properties to
interactions that bind them into atomic nuclei. Quantities that cannot be fully
resolved through experiment, such as the neutron lifetime (whose precise value
is important for the existence of light-atomic elements that make the sun shine
and life possible), may be understood through numerical solutions to QCD. We
directly solve QCD using Lattice Gauge Theory and calculate nuclear observables
such as neutron lifetime. We have developed an improved algorithm that
exponentially decreases the time-to solution and applied it on the new CORAL
supercomputers, Sierra and Summit. We use run-time autotuning to distribute GPU
resources, achieving 20% performance at low node count. We also developed
optimal application mapping through a job manager, which allows CPU and GPU
jobs to be interleaved, yielding 15% of peak performance when deployed across
large fractions of CORAL.Comment: 2018 Gordon Bell Finalist: 9 pages, 9 figures; v2: fixed 2 typos and
appended acknowledgement
Nonequilibrium dynamical mean-field calculations based on the non-crossing approximation and its generalizations
We solve the impurity problem which arises within nonequilibrium dynamical
mean-field theory for the Hubbard model by means of a self-consistent
perturbation expansion around the atomic limit. While the lowest order, known
as the non-crossing approximation (NCA), is reliable only when the interaction
U is much larger than the bandwidth, low-order corrections to the NCA turn out
to be sufficient to reproduce numerically exact Monte Carlo results in a wide
parameter range that covers the insulating phase and the metal-insulator
crossover regime at not too low temperatures. As an application of the
perturbative strong-coupling impurity solver we investigate the response of the
double occupancy in the Mott insulating phase of the Hubbard model to a
dynamical change of the interaction or the hopping, a technique which has been
used as a probe of the Mott insulating state in ultracold fermionic gases.Comment: 14 pages, 9 figure
Dynamical Mean-Field Theory within the Full-Potential Methods: Electronic structure of Ce-115 materials
We implemented the charge self-consistent combination of Density Functional
Theory and Dynamical Mean Field Theory (DMFT) in two full-potential methods,
the Augmented Plane Wave and the Linear Muffin-Tin Orbital methods. We
categorize the commonly used projection methods in terms of the causality of
the resulting DMFT equations and the amount of partial spectral weight
retained. The detailed flow of the Dynamical Mean Field algorithm is described,
including the computation of response functions such as transport coefficients.
We discuss the implementation of the impurity solvers based on hybridization
expansion and an analytic continuation method for self-energy. We also derive
the formalism for the bold continuous time quantum Monte Carlo method. We test
our method on a classic problem in strongly correlated physics, the
isostructural transition in Ce metal. We apply our method to the class of heavy
fermion materials CeIrIn_5, CeCoIn_5 and CeRhIn_5 and show that the Ce 4f
electrons are more localized in CeRhIn_5 than in the other two, a result
corroborated by experiment. We show that CeIrIn_5 is the most itinerant and has
a very anisotropic hybridization, pointing mostly towards the out-of-plane In
atoms. In CeRhIn_5 we stabilized the antiferromagnetic DMFT solution below 3K,
in close agreement with the experimental N\'eel temperature.Comment: The implementation of Bold-CTQMC added and some test of the method
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How to compute Green's Functions for entire Mass Trajectories within Krylov Solvers
The availability of efficient Krylov subspace solvers play a vital role for
the solution of a variety of numerical problems in computational science. Here
we consider lattice field theory. We present a new general numerical method to
compute many Green's functions for complex non-singular matrices within one
iteration process. Our procedure applies to matrices of structure , with
proportional to the unit matrix, and can be integrated within any Krylov
subspace solver. We can compute the derivatives of the solution
vector with respect to the parameter and construct the Taylor expansion
of around . We demonstrate the advantages of our method using a minimal
residual solver. Here the procedure requires intermediate vector for each
Green's function to compute. As real life example, we determine a mass
trajectory of the Wilson fermion matrix for lattice QCD. Here we find that we
can obtain Green's functions at all masses at the price of one
inversion at mass .Comment: 11 pages, 2 eps-figures, needs epsf.st
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