OPP¶

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

Bases: Pair

Oscillating 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.

OPP computes the oscillating pair force on all particles in the simulation state:

\[U(r) = C_1 r^{-\eta_1} + C_2 r^{-\eta_2} \cos{\left(k r - \phi\right)}\]

The potential was introduced in Marek Mihalkovič and C. L. Henley 2012.

Example:

nl = nlist.Cell()
opp = pair.OPP(nl, default_r_cut=3.0)
opp.params[("A", "A")] = {
    "C1": 1.0,
    "C2": 1.0,
    "eta1": 15,
    "eta2": 3,
    "k": 1.0,
    "phi": 3.14,
}
opp.r_cut[("A", "B")] = 3.0

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 OPP:

params¶

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

C1 (float, required) - Energy scale of the first term \(C_1\) \([\mathrm{energy}]\)
C2 (float, required) - Energy scale of the second term \(C_2\) \([\mathrm{energy}]\)
eta1 (float, required) - The inverse power to take \(r\) to in the first term, \(\eta_1\) \([\mathrm{dimensionless}]\).
eta2 (float, required) - The inverse power to take \(r\) to in the second term \(\eta_2\) \([\mathrm{dimensionless}]\).
k (float, required) - oscillation frequency \(k\) \([\mathrm{length}^{-1}]\)
phi (float, required) - potential phase shift \(\phi\) \([\mathrm{dimensionless}]\)

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