ABSTRACT
Since the cosine of 90° is zero, then, for example, a∗ is perpendicular to b and also b∗ is perpendicular to a. If the units of a are angstroms, then the units of a∗ are angstroms−1. Figure 5.1 illustrates the relationship between direct and reciprocal basis vectors in two dimensions. e angle between a and b is γ; the angle between a∗ and b∗ is γ∗. Since a and b are in angstroms and a∗ and b∗ are in inverse angstroms, the directions of the vectors are emphasized, not their relative lengths.
