DFT Investigation of Nuclear 14N Quadrupole Coupling Constants for Four HMX Polymorphs

Density functional theory investigation of ¹⁴N nuclear quadrupole coupling constants (NQCC) for HMX polymorphs was performed. During the calculation of NQCC and asymmetry parameter (η) of β‐HMX, single molecule model is found to be worse than cluster model. The calculated results are more sensitive to the proper model than to the basis set. The calculation for β‐HMX using cluster model at B3LYP/6‐311++G(d,p) level gives better agreement with experiment. This approach was subsequently applied to α, γ, and δ‐HMXs. The difference of simulated ¹⁴N NQR frequency was found. The NQR spectrum is useful for the study of explosive or propellant on their detection, phase transition, and aging process.