  The Nambu-Bethe-Salpeter (NBS) wave function for two nucleons on the lattice
has been shown to yield a non-local and energy-independent nucleon-nucleon (NN)
potential, U(r,r'). In practice, the derivative expansion of U(r,r') is
currently employed to determine the potential at low energies. In this report,
we study the magnitude of non-locality to check the convergence of such a
derivative expansion. With quenched lattice QCD at m_\pi = 530MeV, we compare
the NN potentials at the center of mass energy E ~ 0 MeV and at E ~ 45 MeV. We
also investigate the angular momentum dependence of the spin singlet potential,
by comparing the potentials in 1S0 and 1D2 channels. We find that the
non-locality and the angular momentum dependence in the above energy range are
negligible within statistical errors.
