Infrared Spectra of Liquid Water Studied by Ab initio Methods

The infrared (IR) spectroscopy can probe the dynamic fluctuation of molecule dipoles which are strongly correlated by the H-bond network of liquid water. So far, the quantitative agreement with experiment and theory has not been achieved yet. The difficulty lies in the delicate nature of H-bond structure of water which is affected by not only the directional H-bond strength but also the non-directional van der Waals interaction, which is missing in conventional GGA functional. We performed ab initio molecular dynamics simulations based on the recently developed SCAN meta-GGA functional, which has been proved to be an excellent choice for liquid water (PNAS 114, 10846). We calculated the IR spectra of deuterated water (and ice Ih). Experimental features, such as peaks corresponding to stretching modes, bending mode and libration mode of water molecules, are much better reproduced by the SCAN functional compared with GGA-PBE functional. We further analyze the improvement of computed IR spectra based on the electronic structure improvement provided by SCAN.