Surface adsorption and decomposition mechanisms of cyclotrimethylenetrinitramine (RDX) molecules on the MgH₂ (110) crystal face are investigated in this paper by employing the First-Principles. With the N-NO₂ bond of RDX molecules as a reference, 12 adsorption sites are considered that are vertical (V1-V6) and parallel (P1-P6) to the MgH₂ (110) surface. Results show that these 12 types of adsorption of RDX molecules on the MgH₂ (110) crystal face are all chemical adsorption with high heat release, where the vertical Mg-top position (V1) is the most stable adsorption configuration. In all the 12 types of chemical adsorption, RDX molecules are decomposed, through 4 mechanisms including bis-nitro mono-N-O bond rupture, mono-nitro mono-N-O bond rupture, mono-nitro bis-N-O bond rupture and mono-N-O₂ bond rupture, where the V-type adsorption is due to N-O bond rupture and the P-type adsorption is due to N-NO₂ bond rupture, resulting in RDX decomposition. Secondly, in proximity to the Fermi level, the density of states of the RDX molecule highly coincides with that of the MgH₂ (110) crystal face, which is prone to cause orbital hybridization and RDX decomposition. Also, the density of states in proximity to the Fermi level is mainly contributed by nitro O atoms and ring N atoms of RDX, as well as Mg atoms of the MgH₂ (110) crystal face, and these 3 types of atoms are also active centers for chemical adsorption and decomposition reaction. Finally, an obvious phenomenon of charge transfer is present between Mg atoms in the first layer of the MgH₂ (110) crystal face and O atoms in the nitro group of RDX. Also, the charge change in O and Mg atoms in the V configuration is greater than that in the P configuration, indicating that the V configuration has stronger interaction between RDX and the MgH₂ (110) crystal face, and thus RDX in the V configuration is more prone to decomposition and the V configuration represents a better adsorption mode.

中文翻译：

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第一性原理研究RDX在MgH ₂表面的分解和吸附性能

本文采用第一性原理研究了环三亚甲基三硝胺（RDX）分子在MgH ₂（110）晶面上的表面吸附和分解机理。以RDX分子的N-NO ₂键为参考，考虑了12个吸附点，它们垂直于MgH ₂（110）表面（V1-V6）和平行（P1-P6）。结果表明，RDX分子在MgH ₂上的这12种吸附类型（110）晶面都是具有高散热性的化学吸附，其中垂直的Mg顶部位置（V1）是最稳定的吸附结构。在所有12种化学吸附类型中，RDX分子通过双-硝基单-NO键断裂，单-硝基单-NO键断裂，单-硝基双-NO键断裂和单-NO ₂键四种机理分解。V型吸附是由于NO键断裂而P型吸附是由于N-NO ₂键断裂而导致RDX分解。其次，在费米能级附近，RDX分子的态密度与MgH ₂高度一致（110）晶面，容易引起轨道杂交和RDX分解。同样，费米能级附近的态密度主要由RDX的硝基O原子和环N原子以及MgH ₂（110）晶面的Mg原子贡献，并且这三种类型的原子也都具有活性化学吸附和分解反应中心。最后，在MgH ₂（110）晶面的第一层中的Mg原子与RDX的硝基中的O原子之间存在明显的电荷转移现象。另外，V构型中O和Mg原子的电荷变化大于P构型中的电荷变化，表明V构型在RDX和MgH ₂之间具有更强的相互作用 （110）晶面，因此V构型的RDX更易于分解，并且V构型表示更好的吸附模式。