ForceShiftedLJ

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

Bases: Pair

Force-shifted Lennard-Jones pair force.

Parameters:

ForceShiftedLJ computes the modified Lennard-Jones pair force on every particle in the simulation state.

\[U(r) = 4 \varepsilon \left[ \left( \frac{\sigma}{r} \right)^{12} - \left( \frac{\sigma}{r} \right)^{6} \right] + \Delta V(r)\]
\[\Delta V(r) = -(r - r_{\mathrm{cut}}) \frac{\partial V_{\mathrm{LJ}}}{\partial r}(r_{\mathrm{cut}})\]

The force differs from the one calculated by LJ by the subtraction of the value of the force at \(r_{\mathrm{cut}}\), such that the force smoothly goes to zero at the cut-off. The potential is modified by a linear function. See Toxvaerd et. al. 2011 for a discussion of this potential.

Example:

nl = nlist.Cell()
fslj = pair.ForceShiftedLJ(nlist=nl, default_r_cut=1.5)
fslj.params[("A", "A")] = dict(epsilon=1.0, sigma=1.0)

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 ForceShiftedLJ:

params

The potential parameters. The dictionary has the following keys:

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

  • sigma (float, required) - \(\sigma\) \([\mathrm{length}]\)

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