DIFFUSION ANOMALY IN SILICALITE AND VPI-5 FROM MOLECULAR-DYNAMICS SIMULATIONS
DIFFUSION ANOMALY IN SILICALITE AND VPI-5 FROM MOLECULAR-DYNAMICS SIMULATIONS
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DOI：
10.1021/j100012a060
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发表时间：
1995-03-23
影响因子：
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通讯作者：
YASHONATH, S
中科院分区：
文献类型：
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作者：
BANDYOPADHYAY, S;YASHONATH, S
用分子动力学方法对硅沸石的刚性骨架模型和柔性骨架模型以及磷酸铝VPI-5的刚性骨架模型进行了分子动力学模拟。山梨酸盐-主体相互作用用简单的原子-原子Lennard-Jones相互作用来模拟。结果表明，当伽马系数接近1时，扩散系数出现反常。分子动力学结果证实，对于明显小于通道直径的吸附树脂直径，存在一个线性区域；对于与通道直径相当的吸附树脂直径，则存在一个反常区域。由速度自相关函数的傅里叶变换得到的功率谱表明，在反常区域内，与吸附颗粒直径平行的速度分量的低频分量的强度增加。目前的结果表明，扩散异常的观察与(1)孔结构的几何和拓扑以及(2)宿主材料的性质无关。这一结果与德鲁安及其同事的工作进行了比较，他们在早期的理论和计算方法的基础上提出了“浮动分子”的存在。
Molecular dynamics (MD) simulations on rigid and flexible framework models of silicalite and a rigid framework model of the aluminophosphate VPI-5 for different sorbate diameters are reported. The sorbate-host interactions are modeled in terms of simple atom-atom Lennard-Jones interactions. The results suggest that the diffusion coefficient exhibits an anomaly as gamma approaches unity. The MD results confirm the existence of a linear regime for sorbate diameters significantly smaller than the channel diameter and an anomalous regime observed for sorbate diameters comparable to the channel diameter. The power spectra obtained by Fourier transformation of the velocity autocorrelation function indicate that there is an increase in the intensity of the low-frequency component for the velocity component parallel to the direction of motion for the sorbate diameter in the anomalous regime. The present results suggest that the diffusion anomaly is observed irrespective of (1) the geometry and topology of the pore structure and (2) the nature of the host material. The results are compared with the work of Derouane and co-workers, who have suggested the existence of ''floating molecules'' on the basis of earlier theoretical and computational approaches.