We pay attention to the coupling between the hydrogen network and the intramolecular dynamics, which has been recently highlighted in many experimental and simulation works. The hydrogen-bond strength decreases as the OH vibrational frequency increases or the HOH bending frequency decreases . Specifically, Fujii and Mizuse analyze the relationship between the coordination and the stretching mode frequency. Intermolecular and intramolecular dynamics are analyzed based on the vibrational density of states, which is given as