  An efficient solution of the Dirac Hamiltonian flow equations has been
proposed through a novel expandsion with the inverse of the Dirac effective
mass. The efficiency and accuracy of this new expansion have been demonstrated
by reducing a radial Dirac Hamiltonian with large scalar and vector potentials
to two nonrelativistic Hamiltonians corresponding to particles and
antiparticles, respectively. By solving the two nonrelativistic Hamiltonians,
it is found that the exact solutions of the Dirac equation, for both particles
and antiparticles, can be reproduced with a high accuracy up to only a few
lowest order terms in the expansion. This could help compare and bridge the
relativistic and nonrelativistic nuclear energy density functional theories in
the future.
