Dear Chimera users, To get *Amber prmtop file* corresponding to a *pdb file using Chimera*, I did the following steps: 1] tools -> Amber -> write prmtop 2] In a pop-up window 'save file in chimera', I gave file name, say, aa.prmtop, then clicked save. 3] No charges message appeared, then I clicked 'Assign charges'. 4] In a pop-up window 'Add charge', I selected 'AM1-BCC' in other residues, then clicked ok. 5] In a pop up window 'specify net charge', I selected 'AMI-BCC' in charge method 6] I got 'chimera error' - failure running ANTECHEMBER for residue HIS. Check reply log for details. 7] In reply log, '*Failure running ANTECHEMBER for residue HIS*' seen. Any help in this issue will be a good help for me. Thank you. Mahendra Thapa University of Cincinnati,OH