While ψ Naïve AB is simple to calculate if ψ A and ψ B are known, it lacks two properties that the exact wave function ψ AB must satisfy, namely the wave function is not (fully) antisymmetric (only interchanging the coordinates of electrons belonging to the same molecule will satisfy the antisymmetry condition, provided that ψ A and ψ B are exact wave functions of their respective molecules) nor is it guaranteed that ψ Naïve AB is an eigenfunction of ĤAB (in most cases it will not). We partition this interaction energy (Equation ) in three components: Electron-electron, electron-nuclei and nuclei-nuclei interaction energy components between electrons/nuclei which do not belong to a same molecule (∆E EE AB , ∆E EN AB and ∆E NN AB respectively):