Dear Chimera Developers, First, thank you all for such a wonderful program! Also, thanks to the users' list for such quick, thorough, and always-helpful answers! Second, a little background: I have a gromacs MD simulation (well several, actually) of a small ligand diffusing through a protein. Because the ligand requires the entire simulation to traverse the protein cavity, I was thinking of using the Surfnet tool to accumulate or "build-up" the cavity interface between the ligand and protein using a per-frame python script a la Eric's suggestion in the Dec 2009 [Chimera-users] Surfnet command line thread on this mailing list. I was thinking I could then "prune" the accumulated SurfaceModel using the surfvol.py script available on the http://plato.cgl.ucsf.edu/trac/chimera/wiki/Scripts download page. Now, I can generate a Surfnet surface easily (as Eric points out) for each MD frame using the python commands from Surfnet import interface_surfnet interface_surfnet("LigandAtoms","ProteinAtoms") But how, if possible, can I combine all the individual SurfaceModels into one surface? Also, and not secondarily, does this seem like a reasonable approach to obtain the ligand-protein cavity surface? Thanks again for all your generous support. -- William J. McDonald Postdoctoral Scholar Department of Chemistry and Biochemistry University of California, Santa Cruz