Many-Body Expansion-Based\nQuantum Mechanical Force\nField for Cyclotrimethylene Trinitramine under High Pressure

RDX undergoes pressures of approximately 30–50\nGPa during\ndetonation, leading to significant changes in intermolecular interactions.\nAccurately describing these interactions is crucial for understanding\nthe energy transfer in the detonation process. To address this, this\nwork introduces a many-body expansion-based quantum mechanical force\nfield (MB-QMFF) to accurately describe RDX’s intermolecular\ninteractions under high pressures. Using MB-QMFF, we evaluated various\ndensity functionals and found that the M062X functional with GD3 dispersion\ncorrection provided the highest accuracy. Regarding intermolecular\nforces, two-body interactions were the most significant, with three-body\ninteractions being negligible. Additionally, we investigated intermolecular\nenergy variations at different densities (or pressures). The results\nclearly demonstrate an accurate description of intermolecular interactions\nby the MB-QMFF scheme. Therefore, we believe that the MB-QMFF scheme\ncan serve as a foundation for the development of RDX-specific force\nfields and pave the way for future studies on the detonation process\nof RDX.