Different Ways of Hydrogen Bonding in Water - Why Does Warm Water Freeze Faster than Cold Water?

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• 作者：Yunwen Tao ; Wenli Zou ; Junteng Jia ; Wei Li ; Dieter Cremer
• 刊名：Journal of Chemical Theory and Computation
• 出版年：2017
• 出版时间：January 10, 2017
• 年：2017
• 卷：13
• 期：1
• 页码：55-76
• 全文大小：1384K
• ISSN：1549-9626

文摘

The properties of liquid water are intimately related to the H-bond network among the individual water molecules. Utilizing vibrational spectroscopy and modeling water with DFT-optimized water clusters (6-mers and 50-mers), 16 out of a possible 36 different types of H-bonds are identified and ordered according to their intrinsic strength. The strongest H-bonds are obtained as a result of a concerted push–pull effect of four peripheral water molecules, which polarize the electron density in a way that supports charge transfer and partial covalent character of the targeted H-bond. For water molecules with tetra- and pentacoordinated O atoms, H-bonding is often associated with a geometrically unfavorable positioning of the acceptor lone pair and donor σ^*(OH) orbitals so that electrostatic rather than covalent interactions increasingly dominate H-bonding. There is a striking linear dependence between the intrinsic strength of H-bonding as measured by the local H-bond stretching force constant and the delocalization energy associated with charge transfer. Molecular dynamics simulations for 1000-mers reveal that with increasing temperature weak, preferentially electrostatic H-bonds are broken, whereas the number of strong H-bonds increases. An explanation for the question why warm water freezes faster than cold water is given on a molecular basis.