imporper energy

I couldn’ı understand the meaning of the phrase that I encountered in calculating of the imporper energy, attached below (the number of multiple torsions )

<br>some force fields divide/multiply K by the number of multiple<br> torsions that contain the j-k bond in an i-j-k-l torsion<br><br>ramin<br>


Imagine a moleclue where you have several dihedrals
of the form IJKL, where the JK atoms are the same
in each one, but the I and L are different. You might
have 3 I and 3 L, for a total of 9 possible
dihedrals all with the same JK.

In LAMMPS, you need to enumerate all 9 of them
in your input data file. Each would have a dihedral
type, and each would be evaluated according to
the formula, with a specified K.

In other force fields, I believe they treat this multiplicity
differently, so that K values are weighted by
the multiplicity.