Short-range order

Copper in the short-range order (SRO) regime. Random starting positions (no grain seeding) relaxed with a slightly stiffer bond spring over more steps than the amorphous regime: a well-defined first neighbour shell at 2.55 Å forms, and a bump of second-shell density starts to stand out from the background, but no crystalline patches yet.

Parameters

from ase.build import bulk
import tricor as tc

atoms = bulk("Cu", "fcc", a=3.615)
shell_target = tc.CoordinationShellTarget.from_atoms(atoms, phi_num_bins=90)

cell = tc.Supercell.from_atoms(
    atoms,
    cell_dim_angstroms=(40, 40, 40),
    r_max=10, r_step=0.1, phi_num_bins=90,
    rng_seed=42,
)
cell.generate(
    shell_target,
    num_steps=100,
    grain_size=7.0,
    bond_weight=0.6,
    angle_weight=0.0,
    repulsion_weight=1.0,
    hard_core_scale=0.88,
    nonbond_push_scale=0.65,
    displacement_sigma=0.06,
)

The weak angle spring nudges local coordination toward FCC-like geometry without enforcing any of the four first-shell angles strictly. A nonbond_push_scale of 0.85 places the effective first-shell radius close to, but still slightly inside, the reference pair_peak.

Relaxation trajectory

Interactive 3D viewer of the shell-relaxation trajectory (40 × 40 × 40 Å cell). Drag to rotate, scroll to zoom. Controls below the canvas play, scrub, and change playback speed.

g3 distribution

Measured from the final (post-relaxation) atoms. The heatmap is the reduced three-body density in units of the uniform random reference, where white = 1.0, blue = depleted, red = enhanced. The lower panel shows the pair profile g(r); the shaded amber band marks the first-neighbour shell used as the root-bond integration window for the g3 slice.