The coulomb, exchange-repulsion, induction and dispersion components between 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) molecules were quantitatively derived utilizing symmetry adapted perturbation theory (SAPT), and for the first time the nature of the intermolecular interaction of TATB was unraveled. On this basis, the appropriateness of density functionals for investigation of TATB dimers was also elucidated. The results are shown as follows: (1) In the hydrogen bonded TATB dimers, Coulomb force has an enough ability to counteract exchange-repulsion force and plays a leading role. (2) A reasonable geometry of the gas hydrogen bonded TATB dimer takes on a planar structure whose existence has nothing to do with the dispersion. Therefore, the density functionals, whether or not to include the dispersion, should have a correct prediction of the strong polarization plane structure. (3) In the TATB dimers free of any intermolecular hydrogen bonds, Coulomb force has an inability to resist the exchange-repulsion, but the dispersion performs a key function. (4) In this case, it is impossible for the density functionals without a near short-range dispersion to yield a reasonable geometry for TATB dimers of this kind. Just the opposite, the functional PBE0 with the near short-range dispersion is able to predict correctly a weakly polar “parallel-eclipsed” structure, and the dispersion is responsible for the existence of such a structure, which is a classical dispersion dominated dimer. The dispersion taking up an absolutely leading position originates most likely from the interaction between the π electrons on the two different TATB molecules. (5) For all TATB dimers, dispersion either is remarkable or plays a leading role. However, density functionals either exclude the near short-range dispersion or include partially the dispersion. In this way, it is unlikely that all of current density functionals should derive the accurate interaction energies of the dimers. (6) The geometries similar to those of the TATB dimer in the crystallite will not likely exist stably in gas.

Key words: intermolecular interaction, density functional theory, symmetry adapted perturbation theory, 1,3,5-triamino-2,4,6-trinitrobenzene