Brand Holmann V
MS T085, Applied Physics Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
J Phys Chem B. 2005 Jul 21;109(28):13668-75. doi: 10.1021/jp051045v.
We present a computational study of hydrostatic compression effects on the pentaerythritol tetranitrate (PETN) energetic material up to 22.7 GPa by means of the ab initio all-electron periodic Hartree-Fock quantum mechanical method with the STO-3G Gaussian basis set. We fitted the calculated volume-energy relation to the energy SJEOS polynomial function from which we obtained the compression dependence of the pressure (P), the bulk modulus (B), and its pressure derivative (B'). We also fitted the experimental volume-pressure relation to the pressure SJEOS polynomial function, which allowed us to calculate the experimental bulk modulus (B(exp)) and its pressure derivative (). Our calculated values, B = 6.73 GPa and B' = 24.63, are in reasonable agreement with the values B(exp) = 8.48 GPa and = 14.42 from our fit to the experimental X-ray data and with the value B(exp) = 9.8 GPa that was derived from the experimental elastic constants. In addition, we present a discussion on how the lattice vectors and the internal coordinates (i.e., bond lengths, bond angles, and torsion angles) of the C(CH(2)ONO(2))(4) molecules in the PETN lattice change during hydrostatic compression of the crystal. Our calculated results suggest that the C(CH(2)ONO(2))(4) molecules cannot be considered as being rigid but are in fact flexible, accommodating lattice compression through torsions, bendings in their bond angles, and contractions in their bond lengths. At pressures higher than about 8 GPa, however, both the C(CH(2)ONO(2))(4) molecules and the c lattice vector seem to stiffen somewhat. The a lattice vector does not exhibit this stiffening. As a consequence, the pressure dependence of the c/a ratio shows a minimum at about 8 GPa.
我们采用从头算全电子周期性哈特里 - 福克量子力学方法和STO - 3G高斯基组，对季戊四醇四硝酸酯（PETN）含能材料在高达22.7 GPa的静水压力压缩效应进行了计算研究。我们将计算得到的体积 - 能量关系拟合到能量SJEOS多项式函数，从中获得压力（P）、体积模量（B）及其压力导数（B'）的压缩依赖性。我们还将实验体积 - 压力关系拟合到压力SJEOS多项式函数，从而能够计算实验体积模量（B(exp)）及其压力导数（ ）。我们计算得到的值B = 6.73 GPa和B' = 24.63，与我们根据实验X射线数据拟合得到的值B(exp) = 8.48 GPa和 = 14.42以及从实验弹性常数得出的B(exp) = 9.8 GPa合理一致。此外，我们讨论了在晶体静水压缩过程中，PETN晶格中C(CH(2)ONO(2))(4)分子的晶格矢量和内坐标（即键长、键角和扭转角）如何变化。我们的计算结果表明，C(CH(2)ONO(2))(4)分子不能被视为刚性的，实际上是柔性的，通过扭转、键角弯曲和键长收缩来适应晶格压缩。然而，在高于约8 GPa的压力下，C(CH(2)ONO(2))(4)分子和c晶格矢量似乎都有所变硬。a晶格矢量没有表现出这种变硬现象。因此，c/a比值的压力依赖性在约8 GPa处出现最小值。
