Many-Body Expansion-Based Quantum Mechanical Force Field for Cyclotrimethylene Trinitramine under High Pressure

RDX undergoes pressures of approximately 30–50
GPa during
detonation, leading to significant changes in intermolecular interactions.
Accurately describing these interactions is crucial for understanding
the energy transfer in the detonation process. To address this, this
work introduces a many-body expansion-based quantum mechanical force
field (MB-QMFF) to accurately describe RDX’s intermolecular
interactions under high pressures. Using MB-QMFF, we evaluated various
density functionals and found that the M062X functional with GD3 dispersion
correction provided the highest accuracy. Regarding intermolecular
forces, two-body interactions were the most significant, with three-body
interactions being negligible. Additionally, we investigated intermolecular
energy variations at different densities (or pressures). The results
clearly demonstrate an accurate description of intermolecular interactions
by the MB-QMFF scheme. Therefore, we believe that the MB-QMFF scheme
can serve as a foundation for the development of RDX-specific force
fields and pave the way for future studies on the detonation process
of RDX.