PHYS 94 |
| X-ray and neutron diffraction, vibrational spectroscopy, and X-ray Raman scattering and absorption experiments on water are often interpreted in terms of hydrogen bonding. To this end a number of geometric definitions of hydrogen bonding in water have been developed. While all definitions of hydrogen bonding are to some extent arbitrary, those involving one distance and one angle for a given water dimer are unnecessarily so. In this paper we develop a systematic procedure based on two-dimensional potentials of mean force for defining cut-offs for a given pair of distance and angular coordinates. We also develop an electronic structure-based definition of hydrogen bonding in liquid water, related to the electronic occupancy of the antibonding OH orbitals. This definition turns out to be reasonably compatible with one of the distance-angle geometric definitions. These two definitions lead to an estimate of the number of hydrogen bonds per molecule in liquid SPC/E water of between 3.2 and 3.4. We also used these and other hydrogen bond definitions to examine the dynamics of local hydrogen bond number fluctuations. Time permitting we will discuss implications of this work for vibrational spectroscopy in water. |
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Quantum Mechanics and Statistical Mechanics: Can One Avoid the Other?
8:20 AM-12:00 PM, Monday, August 20, 2007 BCEC -- 158, Oral
Division of Physical Chemistry |