I felt the formula of the primitive translation vectors of the 2d reciprocal lattice hadn't spread out there somehow. (Neither had "reciprocal lattice rods", I thought.) So I wrote it with its derivation here. Aassuming that you already know the formula of the reciprocal lattice vectors in 3d,I shall derive that in 2d. Formulas of the reciprocal lattice vectors in 2D First, the formula of the reciprocal lattice vectors in 3d are given by \( \vec{a^*} = 2\pi \displaystyle \frac{\vec{b} \times \vec{c}}{\vec{a} \cdot (\vec{b} \times \vec{c}) } \), \( \vec{b^*} = 2\pi \displaystyle \frac{\vec{c} \times \vec{a}}{\vec{a} \cdot (\vec{b} \times ...