Every crystalline material packs atoms into one of a small set of repeating unit cells. How tightly they pack (the atomic packing factor) and how many nearest neighbours each atom touches (coordination number) set the material's density, ductility and strength. Removing atoms — vacancy defects — lowers effective packing and weakens local bonding, exactly as described for point defects in materials science.
APF = (n · V_atom) / V_cell
∂C/∂t = D∇²C (Fick's 2nd law — defect/impurity diffusion)
- Crystal structure — SC (APF 52%, coord. 6), BCC (68%, 8), FCC (74%, 12), HCP (74%, 12).
- Lattice size — how many unit cells stack along each axis; camera reframes automatically.
- Vacancy defects — randomly removes a percentage of atoms, lowering effective packing density and average coordination number.
- Bonds — toggles the nearest-neighbour bond rods that visualize the coordination shell.
Real-world use: this is exactly what electron microscopy and X-ray diffraction reveal about metals, ceramics and semiconductors — packing type and defect density directly predict strength, conductivity and diffusion behaviour.