Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, B4-B5 Campus Nord UPC, 08034 Barcelona, Catalonia, Spain.
J Chem Phys. 2010 Feb 21;132(7):074502. doi: 10.1063/1.3305326.
Molecular dynamics simulations have been performed in a wide range of densities along a near critical isotherm of supercritical water in order to reveal the interconnection between the local hydrogen bonding (HB) network and several related dynamic properties. The results obtained have revealed a significant slowing down of reorientational dynamics of the water molecules as the value of the number of hydrogen bond per molecule increases and this is reflected on the increase in the reorientational correlation times. The calculated reorientational times exhibit also an increasing trend by increasing the bulk density, and this effect is more pronounced in the case of the first-order Legendre reorientational correlation functions. A clear nonlinear dependence of the librational mode frequencies of the water molecules on the augmented local density around them has also been revealed. This result could be regarded as an additional support of experimental observations suggesting the use of a nonlinear relation when analyzing the density dependence of spectroscopic peak frequencies in order to extract information about local density augmentation in supercritical fluids. The HB dynamics have been also investigated, revealing a plateau in the calculated HB lifetimes at intermediate and higher liquidlike densities and a small increase at low, gaslike densities.
已经在接近超临界水的近临界等温线上的广泛密度范围内进行了分子动力学模拟，以揭示局部氢键（HB）网络与几个相关动态特性之间的联系。所得结果表明，随着每个分子的氢键数的增加，水分子的重新取向动力学明显减慢，这反映在重新取向相关时间的增加上。通过增加体密度，计算出的重新取向时间也呈现出增加的趋势，而在一阶勒让德重新取向相关函数的情况下，这种效应更为明显。水分子的摆动模式频率与它们周围增强的局部密度之间也存在明显的非线性关系。这一结果可以被视为对实验观察的进一步支持，即建议在分析光谱峰频率对密度的依赖性时使用非线性关系，以提取关于超临界流体中局部密度增加的信息。还研究了 HB 动力学，在中间和更高的液态密度下，计算出的 HB 寿命出现了一个平台，而在低的气态密度下则略有增加。
