Instantaneous normal mode analysis of orientational motions in liquid water: Local structural effects

The effects of local structures on the orientational motions in liquid water in terms of the instantaneous normal mode (INM) analysis were analyzed. The local structures of a molecule in liquid water were characterized by two different kinds of index including, the numbers of the H bonds donated and accepted by the molecule and the asphericity parameter of its Voronoi polyhedron. According to the indices of the local structures, the simulated water molecules were divided into subensembles in two different ways. The results show that by increasing the asphericity, the rotational contribution has a shift toward the high-frequency end in the real spectrum and a decrease in the fraction of the imaginary modes.