Active¶

class hoomd.md.force.Active(filter)¶

Bases: Force

Active force.

Parameters:: filter (hoomd.filter) – Subset of particles on which to apply active forces.

Active computes an active force and torque on all particles selected by the filter:

\[\begin{split}\vec{F}_i = \mathbf{q}_i \vec{f}_i \mathbf{q}_i^* \\ \vec{\tau}_i = \mathbf{q}_i \vec{u}_i \mathbf{q}_i^*,\end{split}\]

where \(\vec{f}_i\) is the active force in the local particle coordinate system (set by type active_force) and \(\vec{u}_i\) is the active torque in the local particle coordinate system (set by type in active_torque.

Note

To introduce rotational diffusion to the particle orientations, use create_diffusion_updater.

Examples:

all = hoomd.filter.All()
active = hoomd.md.force.Active(
    filter=hoomd.filter.All()
    )
active.active_force['A','B'] = (1,0,0)
active.active_torque['A','B'] = (0,0,0)
rotational_diffusion_updater = active.create_diffusion_updater(
    trigger=10)
sim.operations += rotational_diffusion_updater

Note

The energy and virial associated with the active force are 0.

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...

Members inherited from Force:

additional_energy¶: Additional energy term. Read more...

additional_virial¶: Additional virial tensor term \(W_\mathrm{additional}\). Read more...

cpu_local_force_arrays¶: Local force arrays on the CPU. Read more...

energies¶: Energy contribution \(U_i\) from each particle. Read more...

energy¶: The potential energy \(U\) of the system from this force. Read more...

forces¶: The force \(\vec{F}_i\) applied to each particle. Read more...

gpu_local_force_arrays¶: Local force arrays on the GPU. Read more...

torques¶: The torque \(\vec{\tau}_i\) applied to each particle. Read more...

virials¶: Virial tensor contribution \(W_i\) from each particle. Read more...

Members defined in Active:

filter¶

Subset of particles on which to apply active forces.

Type:: hoomd.filter

active_force¶

Active force vector in the local reference frame of the particle \([\mathrm{force}]\). It is defined per particle type and stays constant during the simulation.

Type: TypeParameter [particle_type, tuple [float, float, float]]

active_torque¶

Active torque vector in the local reference frame of the particle \([\mathrm{force} \cdot \mathrm{length}]\). It is defined per particle type and stays constant during the simulation.

Type: TypeParameter [particle_type, tuple [float, float, float]]

create_diffusion_updater(trigger, rotational_diffusion)¶

Create a rotational diffusion updater for this active force.

Parameters:

trigger (hoomd.trigger.trigger_like) – Select the timesteps to update rotational diffusion.
rotational_diffusion (hoomd.variant.variant_like) – The rotational diffusion as a function of time or a constant.

Returns:

The rotational diffusion updater.

Return type:

hoomd.md.update.ActiveRotationalDiffusion