  Tensor force is an important component in the nucleon-nucleon interaction,
nevertheless, the role of the tensor force in the spin properties in finite
nuclei is much less clear. In this report, we mainly focus on our recent
progress on this topic about the relativistic Brueckner-Hartree-Fock theory and
the corresponding tensor effects on the spin-orbit splittings in neutron drops.
This will serve as an important guide for future microscopic derivations of the
relativistic and non-relativistic nuclear energy density functionals.
