228 research outputs found
Accelerating Hybrid Monte Carlo simulations of the Hubbard model on the hexagonal lattice
We present different methods to increase the performance of Hybrid Monte
Carlo simulations of the Hubbard model in two-dimensions. Our simulations
concentrate on a hexagonal lattice, though can be easily generalized to other
lattices. It is found that best results can be achieved using a flexible GMRES
solver for matrix inversions and the second order Omelyan integrator with
Hasenbusch acceleration on different time scales for molecular dynamics. We
demonstrate how an arbitrary number of Hasenbusch mass terms can be included
into this geometry and find that the optimal speed depends weakly on the choice
of the number of Hasenbusch masses and their values. As such, the tuning of
these masses is amenable to automization and we present an algorithm for this
tuning that is based on the knowledge of the dependence of solver time and
forces on the Hasenbusch masses. We benchmark our algorithms to systems where
direct numerical diagonalization is feasible and find excellent agreement. We
also simulate systems with hexagonal lattice dimensions up to
and . We find that the Hasenbusch algorithm leads to a speed up of more
than an order of magnitude.Comment: Corrected Proof in Press in Computer Physics Communication
The Semimetal-Antiferromagnetic Mott Insulator Quantum Phase Transition of the Hubbard Model on the Honeycomb Lattice
The Hubbard model on the honeycomb lattice undergoes a quantum phase
transition from a semimetallic to a Mott insulating phase and from a disordered
to an anti-ferromagnetically phase. We show that these transitions occur
simultaneously and we calculate the critical coupling as well
as the critical exponents and which are
expected to fall into the Gross-Neveu universality class. For this we
employ Hybrid Monte Carlo simulations, extrapolate the single particle gap and
the spin structure factors to the thermodynamic and continuous time limits, and
perform a data collapse fit. We also determine the zero temperature values of
single particle gap and staggered magnetisation on both sides of the phase
transition.Comment: LATTICE2021 proceedings, more details in arXiv:2005.11112 and
arXiv:2105.0693
The Semimetal-Mott Insulator Quantum Phase Transition of the Hubbard Model on the Honeycomb Lattice
We take advantage of recent improvements in the grand canonical Hybrid Monte
Carlo algorithm, to perform a precision study of the single-particle gap in the
hexagonal Hubbard model, with on-site electron-electron interactions. After
carefully controlled analyses of the Trotter error, the thermodynamic limit,
and finite-size scaling with inverse temperature, we find a critical coupling
of and the critical exponent . Under the
assumption that this corresponds to the expected anti-ferromagnetic Mott
transition, we are also able to provide a preliminary estimate
for the critical exponent of the order parameter. We consider
our findings in view of the Gross-Neveu, or chiral Heisenberg,
universality class. We also discuss the computational scaling of the Hybrid
Monte Carlo algorithm, and possible extensions of our work to carbon nanotubes,
fullerenes, and topological insulators
Recent progress in the JARVIS infrastructure for next-generation data-driven materials design
The Joint Automated Repository for Various Integrated Simulations (JARVIS)
infrastructure at the National Institute of Standards and Technology (NIST) is
a large-scale collection of curated datasets and tools with more than 80000
materials and millions of properties. JARVIS uses a combination of electronic
structure, artificial intelligence (AI), advanced computation and experimental
methods to accelerate materials design. Here we report some of the new features
that were recently included in the infrastructure such as: 1) doubling the
number of materials in the database since its first release, 2) including more
accurate electronic structure methods such as Quantum Monte Carlo, 3) including
graph neural network-based materials design, 4) development of unified
force-field, 5) development of a universal tight-binding model, 6) addition of
computer-vision tools for advanced microscopy applications, 7) development of a
natural language processing tool for text-generation and analysis, 8) debuting
a large-scale benchmarking endeavor, 9) including quantum computing algorithms
for solids, 10) integrating several experimental datasets and 11) staging
several community engagement and outreach events. New classes of materials,
properties, and workflows added to the database include superconductors,
two-dimensional (2D) magnets, magnetic topological materials, metal-organic
frameworks, defects, and interface systems. The rich and reliable datasets,
tools, documentation, and tutorials make JARVIS a unique platform for modern
materials design. JARVIS ensures openness of data and tools to enhance
reproducibility and transparency and to promote a healthy and collaborative
scientific environment
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