The intermolecular interactions of three tetranitrotetraazabicyclooctane (bicyclo-HMX) dimers have been calculated by Supermolecular Method (SM) based on HF, MP2, B3LYP and PBE1 calculation with 6-31G* basis set. The interaction energies and their components are derived by symmetry- adapted perturbation theory (SAPT) combining density functional theory (DFT). Although the interactions calculated by MP2 are stronger than those that obtained by the other three SM methods, all of them are less than . Intermolecular interaction of the three dimers show decreasing sequences I＞III＞II because their intermolecular separations at equilibrium geometry show the reverse order 6.58 ? (I)＜6.95 ? (III)＜8.60 ? (II). The interaction energy is lower due to the lost of dispersion calculated by DFT method.

Key words: tetranitrotetraazabicyclooctane (bicyclo-HMX), intermolecular interaction, symmetry-adapted perturbation theory, density functional theory