4 research outputs found
Numerical study of barriers and valleys in the free-energy landscape of spin glasses
We study the problem of glassy relaxations in the presence of an external
field in the highly controlled context of a spin-glass simulation. We consider
a small spin glass in three dimensions (specifically, a lattice of size L=8,
small enough to be equilibrated through a Parallel Tempering simulations at low
temperatures, deep in the spin glass phase). After equilibrating the sample, an
external field is switched on, and the subsequent dynamics is studied. The
field turns out to reduce the relaxation time, but huge statistical
fluctuations are found when different samples are compared. After taking care
of these fluctuations we find that the expected linear regime is very narrow.
Nevertheless, when regarded as a purely numerical method, we find that the
external field is extremely effective in reducing the relaxation times.Comment: 22 pages, 10 figures; Published versio
An experiment-oriented analysis of 2D spin-glass dynamics: a twelve time-decades scaling study
Recent high precision experimental results on spin-glass films ask for a
detailed understanding of the domain-growth dynamics of two-dimensional spin
glasses. To achieve this goal, we numerically simulate the out-equilibrium
dynamics of the Ising spin glass for a time that spans close to twelve orders
of magnitude (from picoseconds to order of a second), in systems large enough
to avoid finite-size effects. We find that the time-growth of the size of the
glassy domains is excellently described by a single scaling function. A single
time-scale controls the dynamics. diverges upon approaching
the critical point. The divergence of is Arrhenius-like,
with a barrier height that depends very mildly on temperature. The growth of
this barrier-height is best described by critical dynamics. As a side product
we obtain an impressive confirmation of universality of the equilibrium
behavior of two-dimensional spin-glasses.Comment: 21 pages, 9 figures. Updated references. Added DOI and Journal re
Highly optimized simulations on single- and multi-GPU systems of 3D Ising spin glass
We present a highly optimized implementation of a Monte Carlo (MC) simulator
for the three-dimensional Ising spin-glass model with bimodal disorder, i.e.,
the 3D Edwards-Anderson model running on CUDA enabled GPUs. Multi-GPU systems
exchange data by means of the Message Passing Interface (MPI). The chosen MC
dynamics is the classic Metropolis one, which is purely dissipative, since the
aim was the study of the critical off-equilibrium relaxation of the system. We
focused on the following issues: i) the implementation of efficient access
patterns for nearest neighbours in a cubic stencil and for
lagged-Fibonacci-like pseudo-Random Numbers Generators (PRNGs); ii) a novel
implementation of the asynchronous multispin-coding Metropolis MC step allowing
to store one spin per bit and iii) a multi-GPU version based on a combination
of MPI and CUDA streams. We highlight how cubic stencils and PRNGs are two
subjects of very general interest because of their widespread use in many
simulation codes. Our code best performances ~3 and ~5 psFlip on a GTX Titan
with our implementations of the MINSTD and MT19937 respectively.Comment: 39 pages, 13 figure