# 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 ```python 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.