I am trying to minimize a protein structure and run into the following error: 'No MMTK name for atom "HND1" in standard residue "HIS"' My .pdb file specifies this atom as ND1, and if I change it to HND1 it still gives me the same error. Does anyone have any suggestions for a solution? The reply log is below: Thanks Jason No incomplete side chains No SEQRES records for COMMD1_C_terminus_c.2.0.pdb (#0) chain A; guessing terminii instead Chain-initial residues that are actual N terminii: GLY 1.A Chain-initial residues that are not actual N terminii: Chain-final residues that are actual C terminii: ASN 73.A Chain-final residues that are not actual C terminii: 42 hydrogen bonds Hydrogens added Charge model: AMBER ff99SB Non-standard atom names: HIS HND1 (HIS 17.A HND1, HIS 22.A HND1) Total charge for #0: -4.000 Correct charges are unknown for 1 non-standard atom names in otherwise standard residues Charges of 0.0 were assigned to the unknown atoms Details in reply log No MMTK name for atom "HND1" in standard residue "HIS"