jaxdem.forces.lennardjones

Finite-range Lennard-Jones interactions with shifted pair energy.

Classes

LennardJones(laws, ...] =, cutoff_ratio)

Lennard-Jones (LJ) 12-6 interaction with a per-pair cutoff and energy shift.

class jaxdem.forces.lennardjones.LennardJones(laws: tuple[~jaxdem.forces.ForceModel, ...]=(), cutoff_ratio: Array = <factory>)

Bases: ForceModel

Lennard-Jones (LJ) 12-6 interaction with a per-pair cutoff and energy shift.

The model reads the material-pair parameter epsilon_eff[mi, mj].

The model derives the length scale \(\sigma_{ij}\) from the particle radii (as in spring.py):

\[\sigma_{ij} = R_i + R_j\]

Potential (for \(r < r_c = c \sigma_{ij}\), with cutoff_ratio \(c=2.5\) by default):

\[U(r) = 4 \epsilon \left[\left(\frac{\sigma}{r}\right)^{12} - \left(\frac{\sigma}{r}\right)^6 \right] - U(r_c)\]

else:

\[U(r) = 0\]

Force (for \(r < r_c\)):

\[\mathbf{F} = 24 \epsilon \left(2 \left(\frac{\sigma}{r}\right)^{12} - \left(\frac{\sigma}{r}\right)^6\right) \frac{1}{r^2}\, \mathbf{r}_{ij}\]

cutoff_ratio: Array

Pair cutoff in units of rad[i] + rad[j]; also sets collider search reach.

static Create(cutoff_ratio: float = 2.5) → LennardJones

Create an LJ law with a positive finite cutoff measured in pair sigma.

search_radii(state: State, system: System) → jax.Array

Conservative search extent for this law’s finite interaction range.

static force(i: int, j: int, pos: jax.Array, state: State, system: System, history: jax.Array, *, advance_history: bool = True, quasistatic: bool = False) → tuple[jax.Array, jax.Array, jax.Array]

static energy(i: int, j: int, pos: jax.Array, state: State, system: System, history: jax.Array) → jax.Array

property required_material_properties: tuple[str, ...]

Names of the material properties this force model needs.

Each name (for example ‘young_eff’ or ‘restitution’) must be present in System.mat_table. Used for validation.