Ewald

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

Bases: Pair

Ewald pair force.

Parameters:

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

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

Ewald computes the Ewald pair force on every particle in the simulation state:

$$U(r) = q_i q_j \left[\mathrm{erfc}\left(\kappa r + \frac{\alpha}{2\kappa}\right) \exp(\alpha r) + \mathrm{erfc}\left(\kappa r - \frac{\alpha}{2 \kappa}\right) \exp(-\alpha r)\right]$$

Call md.long_range.pppm.make_pppm_coulomb_forces to create an instance of Ewald and md.long_range.pppm.Coulomb that together implement the PPPM method for electrostatics.

Example:

nl = nlist.Cell()
ewald = pair.Ewald(default_r_cut=3.0, nlist=nl)
ewald.params[("A", "A")] = dict(kappa=1.0, alpha=1.5)
ewald.r_cut[("A", "B")] = 3.0

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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 Ewald:

params

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

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

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

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