Documentation:worms
From ALPS Algorithms and Libraries for Physics Simulations
Contents |
[edit] Introduction to the worm code
The worm code provides a full generic implementation for Quantum Monte Carlo (QMC) simulations based on the worm algorithms which was invented by N. Prokof'ev and collaborators. Technically, it provides a continuous-time QMC code based on a path integral representation of the partition function.
The current implementation allows to simulate the following models on arbitrary lattices:
- Quantum spin (unfrustrated) models with arbitrary spin size, magnetic field and anisotropy
- (Softcore) bosonic models without a sign problem
Support for simulations with a sign problem could be added if desired
[edit] Running a simulation
An example simulation is discussed in the tutorial.
[edit] Input parameters
The worm code uses the common input parameters discussed here.
[edit] Parameters for experts
In addition, specific simulations parameters can be assigned (use only if you see what it means !):
| Parameter | Default | Meaning |
| SKIP | 1 | the number of Monte Carlo sweeps between each measurement |
| WORMS_PER_KINK | 1 | determines how often a worm shpuld visit a kink on average per sweep. |
| MEASURE_GREEN | false | flag that indicates whether the Green's function should be measured. Don't use - this is untested! |
[edit] Compile time parameters
Furthermore, at compile time you can define the following variables in the file WRun.h
| Parameter | Meaning |
| NONLOCAL | undefine to speed up the code for local interactions. |
| USE_VECTOR | define to use a std::vector instead of a std::list as data structure. |
| USE_SET | define to use a std::set instead of a std::list as data structure. |
[edit] Measurements
The following observables are measured by the worm code application:
| Name | Description |
| Energy | total energy of the system</td> |
| Energy Density | energy per site |
| Density | particle number (for bosonic models)</td> |
| Density^2 | square of the particle number (for bosonic models) |
| Stiffness | stiffness of the system (for bosonic models) |
| Green's function | Green's function (works only for local interactions) |
[edit] License
The license allows the use of the applications for non-commercial scientific use provided that the use of the ALPS applications and libraries is acknowledged and referenced in any scientific publication, as discussed in the license file.
[edit] Questions and request for support
can be addressed to the ALPS user mailing list at comp-phys-alps-users@list.comp-phys.org. We appreciate hearing your requests for additional features and also welcome any contributions to the ALPS project.
[edit] Contributors
The following persons have contributed to the worm application:
© 2002-2004 by Simon Trebst and Matthias Troyer.
