صادق صالح زاده

Unlike covalent interaction which leads to the formation of a classical molecule, non-covalent interaction leads to the formation of molecular clusters. When a pair of non-covalent interactions strengthen each other, it is called cooperative while when they weaken each other they are defined as operating in an anticooperative manner. Cooperativity implies that the sum of at least two interactions is larger than the simple addition of the individual interactions [1, 2]. A quantitative measure of the cooperative effect is made by decomposing the many-body interaction energy (MBIE) of a system of n bodies. But in above method total interaction energy cannot be calculated using a series of defined interactions and we need the many-body term which is not corresponded to any defined type of interaction. In ABC triad system, the appearance of three-body term in any proposed equation for calculation of total interaction energy of a triad means “there is one or more types of interactions but we don't know what they are”. A new equation having four defined interactions that for the first time gives the total interaction energy in a non-cyclic ABC triad without using three-body term is reported [3]. A new method is also proposed for calculating the changes in values of A•••B and B•••C interactions when a non-cyclic triad forms from the corresponding dyads.