Periodic¶

class hoomd.md.external.field.Periodic¶

Bases: Field

One-dimension periodic force.

Periodic computes forces and energies that induce a periodic modulation in the particle concentration. The modulation is one-dimensional and extends along the lattice vector \(\mathbf{a}_i\) of the simulation cell. This force can, for example, be used to induce an ordered phase in a block-copolymer melt.

The force is computed commensurate with the potential energy:

\[U_i(\vec{r_j}) = A \tanh\left[\frac{1}{2 \pi p w} \cos\left( p \vec{b}_i\cdot\vec{r_j}\right)\right]\]

Periodic results in no virial stress due functional dependence on box scaled coordinates.

Example:

periodic = hoomd.md.external.field.Periodic()
periodic.params['A'] = dict(A=1.0, i=0, w=0.02, p=3)
periodic.params['B'] = dict(A=-1.0, i=0, w=0.02, p=3)
simulation.operations.integrator.forces = [periodic]

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 Periodic:

params¶

The Periodic external potential parameters. The dictionary has the following keys:

A (float, required) - Ordering parameter \(A\) \([\mathrm{energy}]\).
i (int, required) - \(\vec{b}_i\), \(i=0, 1, 2\), is the simulation box’s reciprocal lattice vector in the \(i\) direction \([\mathrm{dimensionless}]\).
w (float, required) - The interface width \(w\) relative to the distance \(2\pi/|\mathbf{b_i}|\) between planes in the \(i\)-direction \([\mathrm{dimensionless}]\).
p (int, required) - The periodicity \(p\) of the modulation \([\mathrm{dimensionless}]\).

Type: TypeParameter [particle_type, dict]