高压下硝基甲烷分子温度的密度泛函计算

Density functional theory study on the temperature of nitromethane molecule under pressure

用密度泛函理论在B3LYP/6-311++G(2d,2P)计算水平上对硝基甲烷分子进行了结构优化、频率和热化学分析.发现:在相同温度条件下改变压强,分子熵函数产生了改变,当温度和压强条件相同时,对于不同物质熵函数的改变是相同的.以热力学理论中麦克斯韦关系为基础,通过计算等温过程中分子的熵函数对压强的变化率,用数值拟合方法得到不同压强条件下分子温度的表达式:T=T0+(1-B)[18.3858+0.5392P]V0,式中T0、V0分别表示分子系统初态的温度和体积,T、V分别表示系统在末态的温度和体积,B是体积的压缩比.在选定参数的情况下该表达式可以计算不同压强条件下CHNO含能材料的分子温度.同时,以硝基甲烷为验证,选取基本参数V0和B,计算其在C-J条件对应的爆压14GPa下,分子温度为3461K,对应爱因斯坦温度,相当于3228cm-1的能量,在实验中该能量足以激发硝基甲烷分子内振动能量重新分配过程,有可能激发C-N键的红外振动而引起单分子分解反应的发生.因此,此表达式可用于预测含能材料撞击点火过程单分子分解可能的反应通道.

In the present paper B3LYP method complied with the 6 -311＋＋G（2p, 2d） basis set was em-ployed to investigate the molecular property of nitromethane .Based on a systematic study of the molecular struc-ture, electronic energy , normal vibration mode and thermal chemical functions in nitromethane via the lowest sin -glet, it is found that the decrease of entropy with pressure is evident if we keep the temperature constant .Based on Maxwell relations of the thermodynamic we deduced the fitting equation as follow： T =T0 ＋（ 1 -B ） [18.3858＋0.5392P] V0 , which can calculate the temperature of the energetic molecules under different pres-sures.Further more, the temperature of the nitromethane under 14GPa is 3461K, which equates to 3228cm-1. This energy value could excite the C -H stretching and the intramolecular vibrational redistribution process , the process could generate the decomposition of the molecule .Thus, the fitting equation can expect the decomposed path way of the energetic molecules .