[Chimera-users] Minimizing RNA, no MMTK name for H3"

I'm trying to minimize a few RNA nucleotides using Chimera (Tools / Structure Editing / Minimize Structure) but I get the error message No MMTK name for atom H3" in standard residue C. Chimera adds hydrogens and creates this H3" atom on the 3' terminus (O3' atom) of the RNA. Is there some trick to terminate the 3' end of the RNA so MMTK minimization will work? Here's an example of the problem open 2d1b del ~ :39.B min spec #0 nogui true Thanks! Tom