128 research outputs found
Self-Learning Monte Carlo Method
Monte Carlo simulation is an unbiased numerical tool for studying classical
and quantum many-body systems. One of its bottlenecks is the lack of general
and efficient update algorithm for large size systems close to phase transition
or with strong frustrations, for which local updates perform badly. In this
work, we propose a new general-purpose Monte Carlo method, dubbed self-learning
Monte Carlo (SLMC), in which an efficient update algorithm is first learned
from the training data generated in trial simulations and then used to speed up
the actual simulation. We demonstrate the efficiency of SLMC in a spin model at
the phase transition point, achieving a 10-20 times speedup.Comment: add more refs and correct some typo
Self-Learning Monte Carlo Method in Fermion Systems
We develop the self-learning Monte Carlo (SLMC) method, a general-purpose
numerical method recently introduced to simulate many-body systems, for
studying interacting fermion systems. Our method uses a highly-efficient update
algorithm, which we design and dub "cumulative update", to generate new
candidate configurations in the Markov chain based on a self-learned bosonic
effective model. From general analysis and numerical study of the double
exchange model as an example, we find the SLMC with cumulative update
drastically reduces the computational cost of the simulation, while remaining
statistically exact. Remarkably, its computational complexity is far less than
the conventional algorithm with local updates
Self-Learning Determinantal Quantum Monte Carlo Method
Self-learning Monte Carlo method [arXiv:1610.03137, 1611.09364] is a powerful
general-purpose numerical method recently introduced to simulate many-body
systems. In this work, we implement this method in the framework of
determinantal quantum Monte Carlo simulation of interacting fermion systems.
Guided by a self-learned bosonic effective action, our method uses a cumulative
update [arXiv:1611.09364] algorithm to sample auxiliary field configurations
quickly and efficiently. We demonstrate that self-learning determinantal Monte
Carlo method can reduce the auto-correlation time to as short as one near a
critical point, leading to -fold speedup. This enables to
simulate interacting fermion system on a lattice for the first
time, and obtain critical exponents with high accuracy.Comment: 5 pages, 4 figure
Symmetry Enforced Self-Learning Monte Carlo Method Applied to the Holstein Model
Self-learning Monte Carlo method (SLMC), using a trained effective model to
guide Monte Carlo sampling processes, is a powerful general-purpose numerical
method recently introduced to speed up simulations in (quantum) many-body
systems. In this work, we further improve the efficiency of SLMC by enforcing
physical symmetries on the effective model. We demonstrate its effectiveness in
the Holstein Hamiltonian, one of the most fundamental many-body descriptions of
electron-phonon coupling. Simulations of the Holstein model are notoriously
difficult due to the combination of the typical cubic scaling of fermionic
Monte Carlo and the presence of extremely long autocorrelation times. Our
method addresses both bottlenecks. This enables simulations on large lattices
in the most difficult parameter regions, and evaluation of the critical point
for the charge density wave transition at half-filling with high precision. We
argue that our work opens a new research area of quantum Monte Carlo (QMC),
providing a general procedure to deal with ergodicity in situations involving
Hamiltonians with multiple, distinct low energy states.Comment: 4 pages, 3 figures with 2 pages supplemental materia
Synthesis, Characterization, and Photocatalytic Activity of Zn-Doped SnO 2
Zn-doped SnO2/Zn2SnO4 nanocomposites were prepared via a two-step hydrothermal synthesis method. The as-prepared samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV-vis diffuse reflection spectroscopy, and adsorption-desorption isotherms. The results of FESEM and TEM showed that the as-prepared Zn-doped SnO2/Zn2SnO4 nanocomposites are composed of numerous nanoparticles with the size ranging from 20 nm to 50 nm. The specific surface area of the as-prepared Zn-doped SnO2/Zn2SnO4 nanocomposites is estimated to be 71.53 m2/g by the Brunauer-Emmett-Teller (BET) method. The photocatalytic activity was evaluated by the degradation of methylene blue (MB), and the resulting showed that Zn-doped SnO2/Zn2SnO4 nanocomposites exhibited excellent photocatalytic activity due to their higher specific surface area and surface charge carrier transfer
A new unconventional HLA-A2-restricted epitope from HBV core protein elicits antiviral cytotoxic T lymphocytes
Cytotoxic T cells (CTLs) play a key role in the control of Hepatitis B virus (HBV) infection and viral clearance. However, most of identified CTL epitopes are derived from HBV of genotypes A and D, and few have been defined in virus of genotypes B and C which are more prevalent in Asia. As HBV core protein (HBc) is the most conservative and immunogenic component, in this study we used an overlapping 9-mer peptide pool covering HBc to screen and identify specific CTL epitopes. An unconventional HLA-A2-restricted epitope HBc141–149 was discovered and structurally characterized by crystallization analysis. The immunogenicity and anti-HBV activity were further determined in HBV and HLA-A2 transgenic mice. Finally, we show that mutations in HBc141–149 epitope are associated with viral parameters and disease progression in HBV infected patients. Our data therefore provide insights into the structure characteristics of this unconventional epitope binding to MHC-I molecules, as well as epitope specific CTL activity that orchestrate T cell response and immune evasion in HBV infected patients
- …