Dear UCSF Chimera team, Good morning! I am Sheng Zhang, a graduate student from UC Irvine. First I would like to thank you for developing this useful tool, UCSF Chimera. I have a question regarding minimizing molecule with non-standard amino acids. I modified a linear peptide ligand so it's now a ring containing non-standard amino acids. When I was trying to minimize the ligand while fixing its protein partner, I kept getting error messages like "failure running ANTECHAMBER for residue UNK+THR". The unknown and threonine residues happen to be the residues that I built and modified. Now they are no longer standard/intact amino acid residues and I guess that is why Chimera doesn't like them when trying to minimize the structure. I wonder is there a way to minimize ligand with non-standard amino acid groups? Thank you so much for your time and help! Best wishes, Sheng