However, the GCMC approach still poses some challenges. One results from the fact that the acceptance probability of a given try depends on the desired chemical potential of water, and additional work is typically needed to establish this value for the temperature, pressure, and composition, of the system being simulated. In addition, the GCMC/MD approach generates trajectories with a time-varying number of water molecules, a feature that can complicate bookkeeping. Finally, the probability of accepting a GC water insertion or removal move is typically low in condensed phase systems, so the method can be inefficient.