bond torsion format for cff93 forcefield

dear lammps experts

I want to use coefficients for bond-torsion in lammps with class2 dihedral style.
but the function for bond-torsion is different .
bond-torsion format for class2 dihedral in lammps :
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but the bond-torsion format for cff93 paper (https://pubs.acs.org/doi/10.1021/ja00086a030
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how can I resolve the problem?
thanks

please do some thinking!

a) what is the relevance of the absolute value of energy in classical potentials? and what changes when you add a constant term to a potential function?

b) how does the force with respect to phi change between those two expressions?

the answers should be obvious and requires just a little knowledge of calculus and classical mechanics.

axel.

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the derivative of energy respect to phi in first expression= - ( the derivative of energy respect to phi in second expression )
then ( k1 = - A1 , k2 = - A2 , k3 = - A3 ) .
is it correct?

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