EDM Operator Free from Schiff's Theorem

We present a generalization of Schiff's transformation of electric dipole moments (EDM) in quantum field theory. Under the unitary transformation, the time and parity violating interaction i (ge/2) bar{ψ} σ_{μ ν} γ₅ ψ F^{μ ν} is transformed into a new form, but its nonrelativistic reduction has a unique form to which Schiff's theorem does not apply. The relativistic corrections to the new EDM operator slightly increase the EDM, as given by b₂ (α Z)² with b₂ ~= 2. It is thus seen that the calculation of the EDM with nonrelativistic Hartree-Fock wave functions presents a conservative but reliable estimation for the enhancement factor of the EDM in atoms.