Arul Murugan N
Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, India.
J Chem Phys. 2005 Dec 22;123(24):244514. doi: 10.1063/1.2145678.
The effect of pressure on the structure and reorientational motion of molecules in orientationally disordered (OD) crystalline phase of cubane has been investigated in detail using variable shape molecular simulations in constant-pressure constant-temperature ensemble. Complete orientational ordering occurs at a pressure of 1.0 GPa and the OD phase transforms to an orientationally ordered phase at this pressure. The transition is associated with a kink in the variation of structural parameters such as cell parameters, unit-cell volume, and interaction energy. This transition is also associated with an anomaly in specific heat. Above this transition pressure, the structural quantities display only smaller changes with further increase in pressure. The structure of high-pressure orientationally ordered (HPOO) phase has been characterized using radial distribution functions and orientational distribution function. From detailed analysis of the structure of HPOO phase we conclude that it is isostructural with low-temperature orientationally ordered phase. The OD phase has four times larger compressibility than the HPOO phase.
在恒压恒温系综中使用可变形状分子模拟，详细研究了压力对立方烷取向无序（OD）晶相分子结构和重取向运动的影响。在1.0 GPa的压力下发生完全取向有序化，在此压力下OD相转变为取向有序相。该转变与诸如晶胞参数、单胞体积和相互作用能等结构参数变化中的一个拐点相关。此转变还与比热异常有关。高于此转变压力，随着压力进一步增加，结构量仅显示较小变化。使用径向分布函数和取向分布函数对高压取向有序（HPOO）相的结构进行了表征。通过对HPOO相结构的详细分析，我们得出结论，它与低温取向有序相是同构的。OD相的压缩率比HPOO相大四倍。
