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]

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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 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...

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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]