StochasticRotationDynamics

class hoomd.mpcd.collide.StochasticRotationDynamics(period, angle, kT=None, embedded_particles=None)

Bases: CollisionMethod

Stochastic rotation dynamics collision method.

Parameters:

• period (int) – Number of integration steps between collisions.

• angle (float) – Rotation angle (in degrees).

• kT (hoomd.variant.variant_like) – Temperature for the collision thermostat \([\mathrm{energy}]\). If None, no thermostat is used.

• embedded_particles (hoomd.filter.ParticleFilter) – HOOMD particles to include in collision.

This class implements the stochastic rotation dynamics (SRD) collision rule for MPCD proposed by Malevanets and Kapral. Every period steps, the particles are binned into cells. The particle velocities are then rotated by angle around an axis randomly drawn from the unit sphere. The rotation is done relative to the average velocity, so this rotation rule conserves linear momentum and kinetic energy within each cell.

The SRD method naturally imparts the NVE ensemble to the system comprising the MPCD particles and the embedded_particles. Accordingly, the system must be properly initialized to the correct temperature. A thermostat can be applied in conjunction with the SRD method through the kT parameter. SRD employs a Maxwell-Boltzmann thermostat on the cell level, which generates a constant-temperature ensemble. The temperature is defined relative to the cell-average velocity, and so can be used to dissipate heat in nonequilibrium simulations. Under this thermostat, the SRD algorithm still conserves linear momentum, but kinetic energy is no longer conserved.

Examples:

Collision of MPCD particles.

srd = hoomd.mpcd.collide.StochasticRotationDynamics(period=1, angle=130)
simulation.operations.integrator.collision_method = srd

Collision of MPCD particles with thermostat.

srd = hoomd.mpcd.collide.StochasticRotationDynamics(
    period=1, angle=130, kT=1.0
)
simulation.operations.integrator.collision_method = srd

Collision including embedded particles.

srd = hoomd.mpcd.collide.StochasticRotationDynamics(
    period=20,
    angle=130,
    kT=1.0,
    embedded_particles=hoomd.filter.All(),
)
simulation.operations.integrator.collision_method = srd

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Members inherited from AutotunedObject:

property kernel_parameters

Kernel parameters. Read more...

property is_tuning_complete

Check if kernel parameter tuning is complete. Read more...

tune_kernel_parameters()

Start tuning kernel parameters. Read more...

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Members inherited from CollisionMethod:

embedded_particiles

HOOMD particles to include in collision. Read more...

period

Number of integration steps between collisions. Read more...

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Members defined in StochasticRotationDynamics:

angle

Rotation angle (in degrees)

Example:

srd.angle = 130

Type:

float

kT

Temperature for the collision thermostat \([\mathrm{energy}]\).

Examples:

Constant temperature.

srd.kT = 1.0

Variable temperature.

srd.kT = hoomd.variant.Ramp(1.0, 2.0, 0, 100)

Type:

hoomd.variant.variant_like