integrator command

Purpose

Command for enabling NVE integration of the particles.

Warning

GPU support for this command has not been tested and may not work as expected.

Syntax

integrator keyword value

  • zero or more keyword/value pairs may be appended

  • keyword = particle_group or particle_type (if particle_group is defined, particle_type is obligatory) or non_spherical_integration_scheme or disable

particle_group value = group-id
  group-id = group of particles that are integrated
particle_type value = sphere or multiplespheres or multisphere or superquadric or convex or concave
disable value = 'yes' or 'no'
  yes = integration will be disabled during the next 'simulate' commands
  no = integration is enabled (again)

For non-spherical particles the following additional keywords are available:

non_spherical_integration_scheme value = default or richardson
  or symplectic or predictor_corrector or woodem
Crank_Nicolson_factor value = value of Crank-Nicolson coefficient. 0 will
  fall back to an explicit integration scheme and 1 to an implicit scheme.
  (default: 0.5)
non_spherical_implicit_rotations value = 'yes' or 'no' or 'iterative'
  yes = handle particle rotation in an implicit manner
  no = handle particle rotation in an explicit manner
  iterative = handle particle rotation in an implicit manner and allow to set the number of iterations and the relaxation factor manually
implicit_rotations_iterations value = number of iterations in implicit rotation
  integration. Only valid if 'non_spherical_implicit_rotations iterative' is used.
  (default: 5)
implicit_rotations_relaxation_factor value = relaxation factor in implicit rotation
  integration. Only valid if 'non_spherical_implicit_rotations iterative' is used.
  (default: 0.3)

Examples

integrator particle_group mygroup particle_type sphere
integrator particle_type multisphere
integrator disable yes
integrator non_spherical_integration_scheme richardson Crank_Nicolson_factor 0.4 non_spherical_implicit_rotations iterative implicit_rotations_iterations 6 implicit_rotations_relaxation_factor 0.35

Description

Depending on the previous definition of the particle shape (via the particle_shape command) and the particle template (via the particle_template command) this command automatically selects the appropriate integrator.

Note

If you use the simulate command and do not have special use-cases, the integrator is invoked automatically.

If the ‘disable’ keyword is used with the ‘yes’ value, no further arguments are allowed. This will remove all integration commands which can be useful in coupled simulations where the particles are supposed to remain stationary.

Note

To (re-)enable the integration, you are required to set disable no. Moreover, this setting is not conserved across restarts.

The ‘non_spherical_integration_scheme’ keyword allows to set an integration scheme for non-spherical particle shapes. The default is to use Richardson iterations for multispheres and concave particles and a symplectic scheme for superquadric and convex particles. If not ‘default’ is chosen then the respective scheme will be applied to all particle types. The ‘predictor_corrector’ scheme is a leap-frog predictor corrector scheme and the ‘woodem’ one is taken from Woodem.

Restrictions

This command is currently compatible with the atom styles: “sphere”, “multiplespheres”, “multisphere”, “superquadric”, “convex” and “concave”. In case of the “sphere” style and if a particletemplate/multisphere exists, a nonspherical integrator is chosen, otherwise the sphere integrator is used. The latter is also used for the “granular” style. The “superquadric” and “convexhull” style also use the nonspherical integrator with integration scheme 1 (for superquadrics).

Defaults

disable = no, non_spherical_integration_scheme = default