FOX⁃7在有限温度下的热力学性质的理论计算  

Calculation of Thermodynamic Properties of Energetic 1,1⁃Diamino⁃2,2⁃dinitroethene(FOX⁃7)at the Finite Temperature

作　　者：范俊宇 苏艳[3] 赵纪军[3] FAN Jun-yu;SU Yan;ZHAO Ji-jun(Department of Physics,Taiyuan Normal University,Jinzhong 030619,China;Institute of Computational and Applied Physics,Taiyuan Normal University,Jinzhong 030619,China;Key Laboratory of Materials Modification by Laser,Ion and Electron Beams(Dalian University of Technology),Ministry of Education,Dalian 116024,China)

机构地区：[1]太原师范学院物理系,山西晋中030619 [2]太原师范学院计算物理与应用物理研究所,山西晋中030619 [3]大连理工大学三束材料改性教育部重点实验室,辽宁大连116024

出　　处：《含能材料》2022年第12期1245-1251,共7页Chinese Journal of Energetic Materials

基　　金：科学挑战专题(TZ2016001);山西省高等学校科技创新项目(2021L412);中央高校基本科研业务费专项资金(DUT20ZD207)。

摘　　要：为了研究温度加载下含能材料的基础物性与分子间相互作用机制,基于准简谐近似,采用色散修正的密度泛函理论研究有限温度下FOX‑7的晶体结构和热力学性质。通过引入零点能和温度效应修正可以显著提高实验温度下晶格参数的准确性,计算的晶格参数与实验值的误差在1%以内,在0~500 K温度范围内,FOX‑7晶胞体积随温度的变化与现有实验值相比较为合理,其误差主要源自声子间相互作用的缺失。进一步,计算了不同条件下的热容、熵以及体积模量等基础热力学参数。结果表明:FOX‑7的晶格参数和热膨胀系数均表现出强烈的各向异性,尤其是分子层间方向的膨胀率远高于分子层内方向。当温度达到200 K后,由硝基旋转引起的分子间相互作用变化使得晶体的热膨胀系数开始收缩,进而可能诱发FOX‑7潜在的结构相变。绝热条件下的体模量与实验测量值符合较为合理,且体模量随温度的演化反映了FOX‑7在有限温度下的软化行为。随着温度的升高,计算的热容和熵均逐渐增大,且等容和等压条件下的热容和熵受非谐作用影响表现出明显的数值差异。To study the fundamental physical properties and intermolecular interaction of energetic materials under the loading temperature,the first‑principle calculation was performed combined with zero‑point energy and temperature effect corrections.The accuracy of lattice parameters at experiment temperature(173 K)can be significantly improved,and the deviations be‑tween the calculated lattice parameters and available experimental data are within 1%.The unit cell volume change with temper‑ature is relatively reasonable compared with the experimental value at 0-500 K,and their deviation is mainly from the lack of in‑teractions between phonons.Furthermore,the basic thermodynamic properties such as heat capacity,entropy and bulk modulus were predicted,and the results indicate that the lattice parameters and thermal expansion coefficient of FOX‑7 have strong an‑isotropy in 0-500 K.Especially,the thermal expansion coefficient of interlayer direction is higher than that of inner layer direc‑tion,which is closely related to the molecular configuration and stacking.Importantly,when the temperature reaches 200 K,the shrinkage of thermal expansion coefficient of FOX‑7 is related to the rotation of NO_(2) group.The NO_(2) group would regulate the in‑termolecular interaction by changing the dihedral angle with the molecular plane,thereby triggering potential phase transforma‑tion of FOX‑7.In addition,the bulk modulus under the adiabatic conditions is consistent with the experimental values reasonably,and the evolution of adiabatic bulk modulus with temperature reflects the softening behavior of FOX‑7 at the finite temperature.With the increase of temperature,the calculated heat capacity and entropy increase gradually,showing obvious numerical differences under the constant volume and pressure due to the anharmonic effect.

关 键 词：FOX‑7 热力学性质 准简谐近似 第一性原理计算 

分 类 号：TJ55[兵器科学与技术—军事化学与烟火技术] O64[理学—物理化学]