Use the estimate of the spin–orbit interaction energy at the beginning of Section 1.13 to estimate the strength of the Rashba term. First, show that the Rashba energy is of order (ka_eff)〈HSO〉, where a = a₀/Z_eff is the effective Bohr radius of an atom and Z_eff is defined in Section 1.13. Then estimate the magnitude of this term for an electron with magnitude of its k-vector about one-tenth of the Brillouin zone, for a lattice constant a = 5 Å, and Z_eff = 4.