Dipole

class hoomd.md.pair.aniso.Dipole(nlist, default_r_cut=None)

Bases: AnisotropicPair

Screened dipole-dipole pair forces.

Parameters:

• nlist (hoomd.md.nlist.NeighborList) – Neighbor list

• default_r_cut (float) – Default cutoff radius $[\mathrm{length}]$.

Dipole computes the (screened) interaction between pairs of particles with dipoles and electrostatic charges:

$$\begin{split} U &= U_{dd} + U_{de} + U_{ee} \\ U_{dd} &= A e^{-\kappa r} \left(\frac{\vec{\mu_i}\cdot\vec{\mu_j}}{r^3} - 3\frac{(\vec{\mu_i}\cdot \vec{r_{ji}}) (\vec{\mu_j}\cdot \vec{r_{ji}})} {r^5} \right) \\ U_{de} &= A e^{-\kappa r} \left(\frac{(\vec{\mu_j}\cdot \vec{r_{ji}})q_i}{r^3} - \frac{(\vec{\mu_i}\cdot \vec{r_{ji}})q_j}{r^3} \right) \\ U_{ee} &= A e^{-\kappa r} \frac{q_i q_j}{r} \end{split} \\$$

Note

All units are documented electronic dipole moments. However, Dipole can also be used to represent magnetic dipoles.

Example:

nl = nlist.Cell()
dipole = md.pair.ansio.Dipole(nl, default_r_cut=3.0)
dipole.params[("A", "B")] = dict(A=1.0, kappa=4.0)
dipole.mu["A"] = (4.0, 1.0, 0.0)

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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 inherited from Pair:

nlist

Neighbor list used to compute the pair force. Read more...

mode

Energy smoothing/cutoff mode. Read more...

r_cut

Cuttoff radius beyond which the energy and force are 0. Read more...

r_on

Radius at which the XPLOR smoothing function starts. Read more...

compute_energy()

Compute the energy between two sets of particles. Read more...

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Members defined in Dipole:

params

The dipole potential parameters. The dictionary has the following keys:

• A (float, required) - $A$ - electrostatic energy scale (default: 1.0) $[\mathrm{energy} \cdot \mathrm{length} \cdot \mathrm{charge}^{-2}]$

• kappa (float, required) - $\kappa$ - inverse screening length $[\mathrm{length}^{-1}]$

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

mu

$\mu$ - the magnetic magnitude of the particle local reference frame as a tuple (i.e. $(\mu_x, \mu_y, \mu_z)$) $[\mathrm{charge} \cdot \mathrm{length}]$.

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