The obtained time constants of water in Ho-(DBM) 3 • H 2 O and bulk liquid were 0.151 and 0.155 ps, respectively. CMD calculations with several different potential functions and parameters have yielded different hydrogen-bond time constants ranging from 0.25-0.55 ps for bulk liquid water. The force-field parameters of water referenced in this study are known to overestimate the self-diffusion coefficients by a factor of 3 to 4. This fact is associated with the short lifetime compared with that commonly used in a rigid geometry model such as the simple point-charge water model. In addition, the criteria for judging the hydrogen bonds are somewhat arbitrary, and different criteria will lead to different time constants.