Dear Gmxers, i've trying to develop the topology files for FAD and ADP since the GMX 3.31 odes not have this molecules. Does someone it before? I know that FFGMX has one topology of FAD but are the parameters similar for FF53a61 in GMX 3.3.1? Thanks in advance. Samuel Pita. "Do not wear yourself out to get rich;do not trust your own cleverness. Cast but a glance at riches, and they are gone, for they will surely sprout wings and fly off to the sky like an eagle."(Proverbs 23:4-5) ===================================== SAM