ForceShiftedLJ¶

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

Bases: Pair

Force-shifted Lennard-Jones pair force.

Parameters:

nlist (hoomd.md.nlist.NeighborList) – Neighbor list.
default_r_cut (float) – Default cutoff radius $[\mathrm{length}]$ .
mode (str) – Energy shifting/smoothing mode.

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]