  We study a special two-atom entanglement case in assumed Cavity QED
experiment in which only one atom effectively exchanges a single photon with a
cavity mode. We compute diatom entanglement under position-dependent atomic
resonant dipole-dipole interaction (RDDI) for large interatomic separation
limit. We show that the RDDI, even which is much smaller than the maximal
atomic Rabi frequency, can induce distinct diatom entanglement. The peak
entanglement (PE) reaches a maximum when RDDI strength can compare with the
Rabi frequency of an atom.
