The quantum mechanics (QM) approach is employed in the investigations of the thermal decomposition of RDX molecules, especially for the initial decomposition reaction of single RDX molecule. The first theoretical analysis of the decomposition mechanism for RDX was conducted by Melius and Binkley 8 at the MP4 level of theory. They found that the N-N homolytic cleavage in an RDX molecule is the primary decomposition pathway with a dissociation energy of ~48 kcal/mol. Harris and Lammertsma 9 calculated the potential energy surface at the B3LYP/6-31G* level of theory and identified that the N-NO2 and C-H bonds in RDX are fragile. A mechanism is proposed to initiate the decomposition by N-N bond cleavage and propagate by H atom transfer. A detailed decomposition mechanism was established by Patidar et al. , including HONO elimination, N-NO2 homolysis, reactions with NO, autocatalytic decomposition via HONO and ONNO2 addition, and hydrogen abstraction via NO. In this mechanism, RDX gradually decomposes into N2O, NO2, NO, HCN, CH2O, CO, CO2, H2O, and other small gas-phase products. Recently, Zhang et al. proposed a kinetic model for RDX decomposition. They claimed that the N-NO2 homolysis to form RDR radical is the dominant decomposition pathway of RDX, which subsequently undergoes C-H �-scission and ring-opening reaction. Although the accurate DFT calculations reveal the decomposition of RDX molecules, the current analysis is all derived from single RDX molecules and the potential intermolecular reactions in the condensed phase requires further investigation.