The four trajectories were joined into one, the water molecules and the ACE2 protein were eliminated and a multi-stage process was followed in order to have a trajectory ready to analyze and cluster the major conformational changes for the zone of interaction of the SARS-CoV-2 RBD with ACE2, using the AMBER20 cpptraj module. It was sought to superimpose all the snapshots of the global trajectory to the first one, using as reference atoms for this superposition those C𝛼 of the RBD of the zone of interaction with ACE2 that had the least fluctuations, thus focusing the clustering precisely in those with the largest fluctuations. In a first stage, the trajectory is superimposed to the first photo and the root mean square factor (RMSF) is calculated, then we select for the next superposition the C𝛼 of residues with RMSF < 2 Å in the interaction zone. We then lowered the cutoff to RMSF < 1 Å, and finally the minimum cutoff for RMSF that allowed a reasonable number of residues obeying the criterium was 0.6 Å.