Interpretation of the X-ray spectra of water as evidence for its asymmetric structure has challenged the conventional symmetric nearly-tetrahedral model and initiated an intense debate about the order and symmetry of the hydrogen bond network in water. Here, we present new insights into the nature of local interactions in liquid water obtained using a novel energy decomposition method. Our simulations reveal that while a water molecule forms, on average, two strong donor and two strong acceptor bonds, there is a significant asymmetry in the energy of these contacts - one of which is approximately twice as strong as the other. We demonstrate that this asymmetry is a results of small instantaneous distortions of hydrogen bonds, which appear and relax on a timescale of hundreds of femtoseconds giving the average symmetric structure. Furthermore, we show that the distinct features of the X-ray spectra originate from molecules with high instantaneous asymmetry. Our findings have important implications as they help reconcile the two existing and seemingly opposite symmetric and asymmetric views on the structure of water.

Electronic signature of the instantaneous asymmetry in the first coordination shell in liquid water

245th National Meeting (2013)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.