含能材料感度评估的空间位阻指数算法和程序设计

含能材料的撞击感度可以通过分子动力学模拟获得,然而其计算成本昂贵且受部分材料缺乏合适力场的限制。设计了用于评估含能材料撞击感度的空间位阻指数(Steric Hindrance Index,SHI)的计算算法并开发了相应的计算机程序。该算法压缩原子在晶胞内的坐标以模拟含能材料受到撞击时的形变,对指定的滑移系建立新的空间直角坐标系并旋转晶胞以处理任意撞击方向和滑移系,将旋转后的晶胞内分子根据质心的x坐标进行分层,计算每相邻两分子层在投影区域内的重叠面积,归一化后获得空间位阻指数。根据设计的含能材料空间位阻指数算法,计算了在压缩比为0.1时太安(PETN)、苯并三氧化呋咱(BTF)、奥克托今(RDX)和梯恩梯(TNT)的平均SHI依次为0.8707、0.7940、0.4228和0.0924,与文献中上述材料撞击感度呈降低趋势的结果相符。根据SHI判别含能材料的滑移系敏感性与采用分子动力学模拟的温度、化学反应生成物含量等计算结果的判断一致,而计算成本和方法适用性有较大提高。

Methodology Design for Calculating Steric Hindrance Index as a Descriptor for the Shock Sensitivity of Energetic Materials

Molecular dynamics simulation is an important method to predict the shock sensitivity of energetic materials,yet it is computationally expensive and needs to use force fields that may be unavailable.Here,an algorithm was designed and imple-mented in a computer program in Python for calculating the Steric Hindrance Index(SHI),which is a descriptor for evaluating shock sensitivity.The algorithm 1)compresses the crystal unit cell of an energetic material keeping the molecular unit rigid to simulate deformation under shock;2)establishes a new rectangular coordinate system for the specific slip system and rotates the cell to deal with general shock directions and slip systems;3)assigns molecular units to layers based on the coordinate of their centroid;4)calculates the overlapped area of each two adjacent layers after projection along the slip direction;and 5)obtains SHI by normalization of overlapped areas.For PETN,BTF,RDX,and TNT at a compression ratio of 0.1,the calculated average SHI are 0.8707,0.7940,0.4228,and 0.0924,respectively,which is consistent with the decreasing order of impact sensitivity mentioned in references.SHI classifies the slip systems in line with those based on molecular dynamics simulations,yet with bet-ter computing efficiency and methodological applicability.