Relativistic corrections to the algebra of position variables and   spin-orbital interaction
  In the framework of vector model of spin, we discuss the problem of a covariant formalism \cite{Pomeranskii1998} concerning the discrepancy between relativistic and Pauli Hamiltonians. We show how the spin-induced non commutativity of a position accounts the discrepancy on the classical level, without appeal to the Dirac equation and Foldy-Wouthuysen transformation. 
Alexei A. Deriglazov and Andrey M. Pupasov-Maksimov
quant-ph gr-qc hep-th math-ph math.MP