We do not currently read or write information on improper torsions for amber.
From amber documentation (http://ambermd.org/prmtop.pdf):
Information about improper torsions is stored in DIHEDRALS_INC_HYDROGEN and DIHEDRALS_WITHOUT_HYDROGEN section.
"If the fourth atom is negative, then the torsion is improper."
Currently atom indices are stored in the datalayer with the negative sign discarded. It's not immediately clear why it is stored this way, or if amber actually reads this information....
We do not currently read or write information on improper torsions for amber.
From amber documentation (http://ambermd.org/prmtop.pdf):
Currently atom indices are stored in the datalayer with the negative sign discarded. It's not immediately clear why it is stored this way, or if amber actually reads this information....