ReactionField

class hoomd.md.pair.ReactionField(nlist, default_r_cut=None, default_r_on=0.0, mode='none')

Bases: Pair

Onsager reaction field pair force.

Parameters:

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

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

  • default_r_on (float) – Default turn-on radius \([\mathrm{length}]\).

  • mode (str) – Energy shifting/smoothing mode.

ReactionField computes the Onsager reaction field pair force on all particles in the simulation state.

Reaction field electrostatics is an approximation to the screened electrostatic interaction, which assumes that the medium can be treated as an electrostatic continuum of dielectric constant \(\epsilon_{RF}\) outside the cutoff sphere of radius \(r_{\mathrm{cut}}\). See: Barker et. al. 1973.

By default (use_charge=False), the reaction field potential ignores the particle charges. Two parameters, \(\varepsilon\) and \(\epsilon_{RF}\) are needed. If \(\epsilon_{RF}\) is specified as zero, it will represent infinity:

\[U(r) = \varepsilon \left[ \frac{1}{r} + \frac{(\epsilon_{RF}-1) r^2}{(2 \epsilon_{RF} + 1) r_c^3} \right]\]

When use_charge is set to True, the following formula is evaluated instead:

\[U(r) = q_i q_j \varepsilon \left[ \frac{1}{r} + \frac{(\epsilon_{RF}-1) r^2}{(2 \epsilon_{RF} + 1) r_c^3} \right]\]

where \(q_i\) and \(q_j\) are the charges of the particle pair.

Example:

nl = nlist.Cell()
reaction_field = pair.reaction_field(nl, default_r_cut=3.0)
reaction_field.params[("A", "B")] = dict(epsilon=1.0, eps_rf=1.0)
reaction_field.params[("B", "B")] = dict(
    epsilon=1.0, eps_rf=0.0, use_charge=True
)

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 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...

Members defined in ReactionField:

params

The potential parameters. The dictionary has the following keys:

  • epsilon (float, required) - \(\varepsilon\) \([\mathrm{energy} \cdot \mathrm{length}]\)

  • eps_rf (float, required) - \(\epsilon_{RF}\) \([\mathrm{dimensionless}]\)

  • use_charge (bool, optional) - evaluate pair force using particle charges (default: False)

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