Each host atom in a CCP lattice is surrounded
by and touches 12 nearest neighbors, each at a distance of 2r:
There are six atoms in the central A layer;
There are three atoms in the B layer
above the A layer;
There are three atoms in the C layer below
the A layer.
The six atoms in the B and C layers form a
trigonal
antiprism (also known as a distorted octahedron) around the
central atom; the length of this prism (the distance between the
two equilateral triangular faces) is 2.CPIS.r,
but the length of the long edges of the six isosceles triangular faces
is slightly greater than that value.
