GreenFunctionMonteCarlo

Overview

GreenFunctionMonteCarlo.jl is a Julia package designed for performing Green Function Monte Carlo (GFMC) simulations on lattice models.

Presently, this package treats only Hamiltonians that are free of the sign problem, i.e. whose elements satisfy

\[ H_{x, x'} \leq 0 \quad \forall x \neq x'\]

where $H_{x, x'}$ is the matrix element of the Hamiltonian between two configurations (spins or bosons) $x$ and $x'$.

Installation

To install the package, use the Julia package manager:

using Pkg
Pkg.add(url = "https://github.com/NilsNiggemann/GreenFunctionMonteCarlo.jl.git")

Quick usage example:

using GreenFunctionMonteCarlo, LinearAlgebraö
NSites = 3
Nwalkers = 10
NSteps = 10
Hilbert = BosonHilbertSpace(NSites, HardCoreConstraint())
moves = Bool.(I(NSites)) # each move flips a single spin
offdiagElements = -ones(NSites)
H = localOperator(eachrow(moves), offdiagElements, DiagOperator(x->0), Hilbert)

problem = GFMCProblem(BosonConfig(Hilbert), Nwalkers, ContinuousTimePropagator(0.1); logψ = EqualWeightSuperposition(), H, Hilbert)
Observer = ConfigObserver(BosonConfig(Hilbert), NSteps, Nwalkers) # Observer to measure the energy and configurations
runGFMC!(problem, NoObserver(), 100) #run for 100 steps without observing to equilibrate
runGFMC!(problem, Observer, NSteps) #run for NSteps steps

Contributing

Contributions are welcome! If you encounter any issues or have suggestions for improvements, please open an issue or submit a pull request on the GitHub repository.

License