md.external.field
Overview
Base class external field force. |
|
Electric field force. |
|
One-dimension periodic force. |
Details
External field forces.
- class hoomd.md.external.field.Electric
Electric field force.
Electric
computes forces, and virials, and energies on all particles in the in the simulation state with consistent with:\[U_i = - q_i \vec{E} \cdot \vec{r}_i\]where \(q_i\) is the particle charge and \(\vec{E}\) is the field vector. The field vector \(\vec{E}\) must be set per unique particle type.
- E
The electric field vector \(\vec{E}\) as a tuple \((E_x, E_y, E_z)\) \([\mathrm{energy} \cdot \mathrm{charge}^{-1} \cdot \mathrm{length^{-1}}]\).
Type:
TypeParameter
[particle_type
,tuple
[float
,float
,float
]]
Example:
# Apply an electric field in the x-direction e_field = external.field.Electric() e_field.E['A'] = (1, 0, 0)
- class hoomd.md.external.field.Field
Base class external field force.
External potentials represent forces which are applied to all particles in the simulation by an external agent.
Warning
This class should not be instantiated by users. The class can be used for
isinstance
orissubclass
checks.
- class hoomd.md.external.field.Periodic
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.- 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
]
Example:
# Apply a periodic composition modulation along the first lattice vector periodic = 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)