 F_{S,{\boldsymbol{k}}_{\parallel}; B, {\boldsymbol{k}}',0n' } &= \big<{\boldsymbol{\Psi}}_{S, {\boldsymbol{k}}_{ \parallel}} \big|   e^{ik_z' z} \big| {\boldsymbol{\Psi}}_{B, {\boldsymbol{k}}', 0n'} \big>, 