The density derived from CMD at 153 K was in agreement with the experimental results within a 5% error, which indicates that the COMPASS force field has reasonable accuracy. The mean Ho-ow distance derived from CMD at 153 K was greater than those obtained using PBE and DFT-D3. This difference can be explained by the thermal expansion of the lattice; indeed, the lattice constant c obtained by CMD was larger than the values obtained from PBE and DFT-D3. The cell shape derived from CMD with all degrees of freedom can reproduce the trigonal (R3 space group) lattice. This shows that the optimization including the six components of the stress tensor was working well. The probability density of hw in the water molecules was calculated from the H position from a 100-ps simulation run to visualize the three-dimensional locations of the water molecules. The yellow-colored volume in Fig. shows a high-probability-density isosurface of hw in a column along the c axis. The DBM and Ho atoms, of which the atomic balls are indicated as their average positions during the simulation run, are also displayed to indicate the relative arrangement of the water molecules. The shape of the isosurface is triangular rather than circular, meaning that there is not free rotation; this is due to strong interaction with the o1= in the DBM. The preferential positioning of hw in water toward o1= with 1/3 occupancy was revealed for La(III) aqua-tris(dibenzoylmethane) by SC-XRD, and this is in agreement with the shape of the isosurface in Fig. . Since the average positions of Ho and ow are regularly aligned along the c axis, stationary vibrational motion of Ho and ow was found at these positions in the crystal structure. Translational motion of water molecules is suppressed, and they have only rotational degrees of freedom. This motion is completely different from that of bulk water, which includes translational motion. These unique dynamics will be discussed later in relation to the hydrogen-bonded kinetic analysis.