tVMC - Time Dependent Variational Monte Carlo

Time-dependent Variational Monte Carlo code for bosonic many-body systems in continuous space.

Source code used in:

• Mathias Gartner, Ferran Mazzanti, Robert E. Zillich
  "Time-dependent variational Monte Carlo study of the dynamic response of bosons in an optical lattice"
  SciPost Phys. 13, 025 (2022)
  https://scipost.org/10.21468/SciPostPhys.13.2.025
• Mathias Gartner, PhD thesis
  "Monte Carlo simulations of non-equilibrium dynamics in bosonic many-body systems"
  https://epub.jku.at/obvulihs/id/8568071
• Mathias Gartner, David Miesbauer, Michael Kobler, Julia Freund, Giuseppe Carleo, Robert E. Zillich
  "Interaction quenches in Bose gases studied with a time-dependent hypernetted-chain Euler-Lagrange method"
  https://arxiv.org/abs/2212.07113
• Mathias Gartner, Master thesis
  "Implementation and Application of the Time Dependent Variational Monte Carlo method in real and imaginary time"
  https://epub.jku.at/obvulihs/2581938

Building from source using Makefile

This program uses MPI for multiprocess execution. You may need to specify options int the Makefile according to the machine your are using for compilation, eg.

• CXX = {mpic++, mpicxx, ...}
• C++ standard >= -std=c++17
• build directory (default is ./build)

Run a simulation

The simulation config file needs to be provided as the first parameter to the program, eg:

./build/TDVMC ./config/Bosons1D_quench.config

Start the program with multiple processes using the required MPI command on the host machine, eg:

mpirun -np 250 ./build/TDVMC ./config/Bosons1D_quench.config

mpiexec -perhost 250 ./build/TDVMC ./config/Bosons1D_quench.config

Configuration file for simulation run

• config files are in JSON format
• example config file can be found in directory config/examples/
• there is also a README file config/examples/README.md with explanation for all the fields in the config
• at the end of every simulation a file AAfinish_tVMC.config is generated in the simulation directory. This file contains the final parameters and can be used in a subsequent simulation (eg. for further imaginary time propagation if parameters are not converged, for real time propagation following an imaginary time propagation, for continuing real time simulations, ...).

Running your first tVMC simulation

To start your first tVMC simulation you can do the following steps:

• download the whole project
• open a terminal and navigate to the project directory
• type make to build the project
• specify an existing directory as OUTPUT_DIRECTORY in the file ./config/examples/LiebLinigerGroundState.config
• run the program on eg. 8 CPU cores with mpirun -np 8 ./build/TDVMC ./config/examples/LiebLinigerGroundState.config

The most advanced PhysicalSystem implemetations are

• InhContactBosons: Bosons in 1D with contact interaction and an external potential. Periodic boundary conditions. Wavefunction has single particle and pair correlation parts
• BosonMixtureCluster: Bosonic mixtures in 3D. Used for ground state optimization of few-body clusters. Piecewise defined Jastrow wavefunction.
• Bosons1D: Bosons in 1D with arbitrary interaction potential. Homogeneous system with periodic boundary conditions. Wavefunction has only pair correlations.
• Bosons1DMixture: Bosonic mixtures in 1D with arbitrary interaction potential. Homogeneous system with periodic boundary conditions. Wavefunction has only pair correlations.

Adding new types of PhysicalSystems

To simulate new types of physical systems a new class has to be added in src/PhysicalSystems which implements the interface src/PhysicalSystems/IPhysicalSystem.h. This new class then needs to be registed in src/TDVMC.cpp with the following steps:

• include the class via #include "PhysicalSystems/NewSystem.h"
• add initialization code in method InitializePhysicalSystem()
• add file output specifications in method WriteGridFiles() and WriteAdditionalObservablesToFiles()
• optional: add code for local testing in main()

External resources

• JSON parser: https://github.com/open-source-parsers/jsoncpp
• Eigen library: https://eigen.tuxfamily.org