Hi all Can anybody please explain me or tell me where I can find an explanation for the variable "fr->fshift[*]" (with *=t1,t2,t3,CENTRAL) in subroutines "do_dih_fup" and "angles" in file bondfree.c ? And an explanation for its arguments t1,t2,t3,CENTRAL ? Thank you very much Daniele Bemporad