In this work, a new equation consist of AB, BC, ABC, and ABC interactions is proposed for calculating the total interaction energy of noncyclic ABC triads. New equations are also proposed for calculating the changes in values of AB and BC interactions on the formation of triad from the corresponding dyads. The advantages of equations proposed here in comparison with many-body interaction energy approach are discussed. All proposed equations were tested in F3MLiNCHHLH and F3MLiHLHHCN (M5C, Si; L5Be, Mg) as well as H3NXYHF (X, Y5F, Cl, Br) noncyclic ABC triads. The data show that the total cooperativity of triad correlates well with the sum of the changes in values of AB and BC interactions calculated through new equations proposed here.
