amber torsion energy

[Letif Mones]

Hi,

I did a molecular mechanical calculation in cp2k using an amber topology file (force field: amber99). When I checked the bonded energy terms I found that the bond and angle terms are correct but the dihedral energy is twice as the energy calculated by sander. I think the reason is that in the amber FF the form of the torsion potential is: K / 2 * [ 1 + cos[ M*PHI - PHI0 ] ] while cp2k uses the form of  K * [ 1 + cos[ M*PHI - PHI0 ] ].
So should not the torsion force constant read from an amber topology file be multiplied by 0.5 (and the improper one too as it has the same form)?

Letif