Hi, I am trying to build an eight alanine residue peptide capped at either end with ACE and NAC. However, when I use pdb2gmx it gives me the following error: Fatal error: atom N not found in residue 1ACE while combining tdb and rtp The error doesn't make a whole lot of sense since there is atom N in ACE. If you have any ideas any help would be great. Thanks alot Erik Storm RPI