Molecular dynamics investigation of the disordered crystal structure of hexagonal LiBH4.
Molecular dynamics investigation of the disordered crystal structure of hexagonal LiBH4.
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DOI：
10.1039/c3cp44520h
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发表时间：
2013-05
期刊：
影响因子：
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通讯作者：
Philippe C. Aeberhard;K. Refson;W. David
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文献类型：
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作者：
Philippe C. Aeberhard;K. Refson;W. David
采用从头算分子动力学方法对六方相固体硼氢化锂（LiBH 4）的低温相和高温相的晶体结构进行了研究。模拟了200-535 K的温度范围，目的是详细描述高温结构中的无序。的硼氢化物单元（BH 4（-））的重定向运动的机制和动力学的确定，并与公布的中子散射实验是一致的，它被发现，旋转扩散率增加了一个数量级的相变温度。平均平衡取向的特征在于取向的广泛分布，并且在明确定义的取向之间不发生再取向跳跃。此外，分裂的位置与部分占用的锂和硼原子被发现（与以前的理论研究一致），这与无序的BH 4（-）的平衡取向分布一起，导致的结论是，正确的晶体学空间群的高温相是P63/mmc，而不是P63 mc。
The crystal structure of the hexagonal phase of solid lithium borohydride (LiBH4) is studied by ab initio molecular dynamics simulations of both the low and high-temperature phases. A temperature range of 200-535 K is simulated with the aim of characterising the disorder in the high-temperature structure in detail. The mechanism and kinetics of the reorientational motion of the borohydride units (BH4(-)) are determined and are consistent with published neutron scattering experiments; it is found that rotational diffusivity increases by an order of magnitude at the phase transition temperature. The average equilibrium orientation is characterised by a broad distribution of orientations, and reorientational jumps do not occur between sharply defined orientations. In addition, split positions with partial occupancy for the lithium and boron atoms are found (in agreement with previous theoretical studies), which, together with the disordered BH4(-) orientational distribution in equilibrium, lead to the conclusion that the correct crystallographic space group of the high-temperature phase is P63/mmc rather than P63mc.