Currently, I have these commands to calculate the closest 5 :SIA out of 45 to a binding site each frame parm ../2_md/CPLX_Neut_Sol.parm7 trajin ../2_md/10.1.produ.nc rms :1-1469 first # align receptor closest 5 :132-134 solventmask :SIA closestout SIA2ChainA_Binding_sites.dat name SIA run exit The output file contains Frame Molecule Distance FirstAtom# which to my understanding, the distance is from the :SIA atom closest to the center of mass of the residues :132-134. 1. Is there some way to do the distance from center of mass :SIA to center of mass residues instead? * ex: [distance of closest :SIA atom to residues] > [distance of :SIA center of mass to residues] 2. Is there a way to do RMSD calculation of those selected closest ligands to a pdb reference? I was thinking along the lines of "for FRAME in" maybe? Thank you, Alex