Elastic constants of ice I_h as described by semi-empirical water models

Using molecular dynamics simulations, we compute the elastic constants of ice I_h for a set of 8 frequently used semi-empirical potentials for water, namely, the rigid-molecule SPC/E, TIP4P, TIP4P2005, TIP4P/Ice, and TIP5P models, the flexible-molecule qTIP4P/Fw and SPC/Fw models, and the coarse-grained atomic mW potential. In quantitative terms, the mW description gives values for the individual stiffness constants that are closest to the experiment, whereas the explicit-proton models display substantial discrepancies. On the other hand, in contrast to all explicit-proton potentials, the mW model is unable to reproduce central qualitative trends such as the anisotropy in Young's modulus and the shear modulus. This suggests that the elastic behavior of ice I_h is closely related to its molecular nature, which has been coarse-grained out in the mW model. These observations are consistent with other recent manifestations concerning the limitations of the mW model in the description of mechanical properties of ice I_h.