Oscillations in the electrostatic energy gap [ΔVelec(t)] for electron transfer from the primary electron donor (P) to the adjacent bacteriochlorophyll (B) in photosynthetic bacterial reaction centers are examined by molecular-dynamics simulations. Autocorrelation functions of ΔVelec in the reactant state (PB) include prominent oscillations with an energy of 17 cm-1. This feature is much weaker if the trajectory is propagated in the product state P+B-. The autocorrelation functions also include oscillations in the regions of 5, 80 and 390 cm-1 in both states, and near 25 and 48 cm-1 in P+B-. The strong 17-cm-1 oscillation could involve motions that modulate the distance between P and B, because a similar oscillation occurs in the direct electrostatic interactions between the electron carriers.