In summary, Mms dimers show larger interaction energies than Phe or Tyr dimers. We also observed that the dipole of each mimosine ring is 9.7 D, which would explain the strong interaction energy in these stacked structures and the reorientation from parallel to antiparallel conformation in the optimization procedure, in the absence of explicit water molecules. Therefore, there is a inherent preference for an antiparallel orientation of both Mms rings. However, the presence of explicit water molecules and the resultant hydrogen bonding network can lead to a substantial stabilization of the parallel orientation.