Nearest Neighbor, Next Nearest Neighbor
					Index
	The diagram shows the unit cell of a body-centered-cubic crystal. The atoms behave as hard spheres and touch along the < 1 1 1 > directions. The blue atom at the cube corner has the red atom as one of 8 nearest-neighbors in the infinite three dimensional structure. These are situated a distance r0 central blue atom. The green atom is at one of the next-nearest-neighbor locations of the structure. There are six sites of this type located at a distance of 2r0/(3)0.5 from the central blue atom.