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 :

but the bond-torsion format for cff93 paper (https://pubs.acs.org/doi/10.1021/ja00086a030

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.

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?