Real crystals are never perfect. Point defects — a missing atom (vacancy) or a squeezed-in extra atom (interstitial) — and line defects (edge dislocations) locally distort the regular cubic lattice. The atoms around each defect shift from their ideal sites to relax the extra or missing volume, storing elastic strain energy in the surrounding bonds.
u(x,y) from elasticity theory, built from the Burgers vector and Poisson's ratio.Dislocations are what make metals ductile: applying stress lets dislocation lines glide through the lattice one atomic row at a time, which takes far less energy than shearing an entire perfect crystal plane at once. Materials engineers deliberately introduce dislocations (via cold-working) or pin them (via alloying) to tune a metal's strength and ductility.
An interactive 3D cubic crystal lattice: switch between a vacancy, an interstitial atom and an edge dislocation, and watch neighbouring atoms shift from their ideal sites under real elastic displacement fields.
Point defects (vacancy, interstitial) distort the lattice with an isotropic 1/r² field; the edge dislocation uses the classical elasticity displacement equations built from the Burgers vector and Poisson's ratio. Atom colour encodes local strain.
Pick a defect type, resize the lattice block, and raise the thermal vibration slider to jiggle atoms like heating the crystal. Toggle the strain color map to compare raw geometry against the displacement heat-map. Drag to orbit, scroll to zoom.
Dislocations let metals deform plastically by gliding one atomic row at a time — far cheaper energetically than shearing a whole crystal plane, which is why real metals are ductile instead of brittle.