Nonrelativistic derivation of the charge current of the Pauli equation using velocity operators

There is a single procedure, using velocity operators, for finding the charge current for both the Schroedinger and Dirac equations. However, this procedure is not directly applicable to the derivation of the charge current of the Pauli theory, which is usually carried out via non-relativistic approximation of the Dirac current. It is shown how the canonical velocity operator method does lead to the current of the Pauli theory when applied to a spin model of Bopp and Haag