摘要
用密度泛函理论 (DFT)B3LYP方法 ,取 6 - 31G 基组 ,求得环四甲撑四硝胺分子的几何构型、电子结构、IR谱和 2 98～ 12 0 0K的热力学性质 .全优化几何构型和电子结构均具有Ci 对称性 .在相邻原子之间以N -NO2 键的Mulliken集居数最小 ,表明其间电子分布较少 ,预示其为热解和起爆的引发键 .
The compound octahydro - 1,3,5,7 - tetranitro - 1,3,5,7 - tetrazocine is a well known energetic material called cyclotetramethylene - tetranitramine ( commonly known as HMX in the explosives field). It is an eight - numbered cyclic nitramine with best comprehensive properties and with applications ranging from explosives and rocked propellants to automobile air bags. It is unusual among high explosives as it has four readily formed and well - recognized polymorphs. beta - HMX is the thermodynamically stable from under ambient condition. Despite the many experimental investigations, very few theoretical studies have previously been reported for HMX. The high accurate calculation for HMX has been carried out based on ab initio quantum mechanics. Geometry optimization and normal - mode analysis of HMX in beta form are performed using nonlocal density functional theory ( DFT) method. The density functional used in this study is B3LYP and the basis set employedis 6 - 31G*. Normal - mode analyses are used to characterize the stable point and to determine harmonic vibrational frequencies for beta - HMX conformer. The molecular geometry, electronic structures, IR spectra and thermodynamic properties are obtained. The fully optimized geometric parameters and the net electric charges on atoms all have C-i symmetric property. C - N bond lengths are among 0.144 similar to 0.148 nm. This indicates that all cyclic C - N bonds are single bond. The N - NO2 bond Mulliken population is the smallest among the bonding atoms. The fact indicates that there are less electronics between them and predicts that this bond is an initial bond for pyrolysis and explosive. The IR spectra are in good agreement with the corresponding experiment data. Half of the 78 harmonic vibrational frequencies for beta - HMX are IR active and belong to Au representation, the rest are Raman active and belong to Ag representation. The calculated standard thermodynamic functions, heat capacities at standard condition C-p,m(0) standard entropy S-m(0) and standard enthalpy H-m(0) between 298 similar to 1200 K increase with the increasing temperature. These functions are helpful to further study on the reaction and properties for HMX.
基金
国防科工委基础研究项目~~
