ActiveRotationalDiffusion

class hoomd.md.update.ActiveRotationalDiffusion(trigger, active_force, rotational_diffusion)

Bases: Updater

Updater to introduce rotational diffusion with an active force.

Parameters:

• trigger (hoomd.trigger.trigger_like) – Select the timesteps to update rotational diffusion.

• active_force (hoomd.md.force.Active) – The active force associated with the updater can be any subclass of the class hoomd.md.force.Active.

• rotational_diffusion (hoomd.variant.variant_like) – The rotational diffusion as a function of time.

ActiveRotationalDiffusion works directly with hoomd.md.force.Active or hoomd.md.force.ActiveOnManifold to apply rotational diffusion to the particle quaternions $\mathbf{q}_i$ in simulations with active forces. The persistence length of an active particle’s path is $v_0 / D_r$.

In 2D, the diffusion follows $\delta \theta / \delta t = \Gamma \sqrt{2 D_r / \delta t}$, where $D_r$ is the rotational diffusion constant and the $\Gamma$ unit-variance random variable.

In 3D, $\hat{p}_i$ is a unit vector in 3D space, and the diffusion follows $\delta \hat{p}_i / \delta t = \Gamma \sqrt{2 D_r / \delta t} (\hat{p}_i (\cos \theta - 1) + \hat{p}_r \sin \theta)$, where $\hat{p}_r$ is an uncorrelated random unit vector.

When used with hoomd.md.force.ActiveOnManifold, rotational diffusion is performed in the tangent plane of the manifold.

Tip

Use hoomd.md.force.Active.create_diffusion_updater to construct a ActiveRotationalDiffusion instance.

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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 TriggeredOperation:

trigger

The trigger to activate this operation. Read more...

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Members defined in ActiveRotationalDiffusion:

active_force

The active force associated with the updater. This is not settable after construction.

Type:

hoomd.md.force.Active

rotational_diffusion

The rotational diffusion as a function of time.

Type:

hoomd.variant.Variant