  We have numerically calculated the single band Wannier functions for
interacting Bose gases in optical lattices with a self-consistent approach. We
find that the Wannier function is broadened by repulsive atom interaction. The
tunneling parameter J and on-site interaction U computed with the broadened
Wannier functions are found to change significantly for different atomic number
per site. Our theory can explain the nonuniform atomic clock shift observed in
[Campbell et al., Science 313, 649 (2006)].
