Molecular Structures, Dipole Moments, and Electronic Properties of β‑HMX under External Electric Field from First-Principles Calculations

In
order to investigate the impact of an external electric
field
on the sensitivity of β-HMX explosives, we employ first-principles
calculations to determine the molecular structure, dipole moment,
and electronic properties of both β-HMX crystals and individual
β-HMX molecules under varying electric fields. When the external
electric field is increasing along the [100], [010], and [001] crystallographic
directions of β-HMX, the calculation results indicate that an
increase in the bond length (N1–N3/N1′–N3′)
of the triggering bond, an increase in the main Qnitro (N3, N3′) value, an increase in the minimum
surface electrostatic potential, and a decrease in band gap all contribute
to a reduction in its stability. Among these directions, the [010]
direction exhibits the highest sensitivity, which can be attributed
to the significantly smaller effective mass along the [010] direction
compared with the [001] and [100] directions. Moreover, the application
of an external electric field along the Y direction
of the coordinate system on individual β-HMX molecules reveals
that the strong polarization effect induced by the electric field
enhances the decomposition of the N1–N3 bonds. In addition,
due to the periodic potential energy of β-HXM crystal, the polarization
effect of β-HMX crystal caused by an external electric field
is much smaller than that of a single β-HXM molecule.

为探究外电场对β-HMX炸药感度的影响，本研究采用第一性原理计算方法，表征了不同外电场条件下β-HMX晶体与单分子β-HMX的分子结构、偶极矩及电子性质。当外电场沿β-HMX的[100]、[010]与[001]晶向逐渐增强时，计算结果显示：引发键N1–N3/N1′–N3′的键长增长、硝胺基特征位点（N3、N3′）的Q值升高、表面最小静电电势提升，以及带隙降低，均会导致体系稳定性下降。在上述三个晶向中，[010]方向对应最高的感度，这可归因于沿[010]方向的有效质量远小于[100]与[001]方向。此外，在坐标系Y方向上对单分子β-HMX施加外电场时，电场诱导的强极化效应会促进N1–N3键的分解。另外，由于β-HXM晶体具有周期性势能，外电场对β-HMX晶体的极化效应远弱于单分子β-HMX分子。