We present a new method for isothermal rigid body simulations using the quaternion representation and Langevin dynamics. It can be combined with the traditional Langevin or gradient (Brownian) dynamics for the translational degrees of freedom to correctly sample the canonical distribution in a simulation of rigid molecules. We propose simple, quasisymplectic second-order numerical integrators and test their performance on the TIP4P model of water. We also investigate the optimal choice of thermostat parameters.

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Bradford Scholars -how to deposit your paper Overview Copyright check• Check if your publisher allows submission to a repository.• Use the Sherpa RoMEO database if you are not sure about your publisher's position or email openaccess@bradford.ac.uk.

We employ the cleaving approach to calculate directly the ice Ih-water interfacial free energy for the simple models of water, TIP4P, TIP4P-Ew, and TIP5P-E, with full electrostatic interactions evaluated via the Ewald sums. The results are in good agreement with experimental values, but lower than previously obtained for TIP4P-Ew and TIP5P-E by indirect methods. We calculate the interfacial free energies for basal, prism, and {112̅0} interfaces and find that the anisotropy of the TIP5P-E model is different from that of the TIP4P models. The effect of including full electrostatic interactions is determined to be smaller than 10% compared to the water models with damped Coulomb interactions, which indicates that the value of the ice-water interfacial free energy is determined predominantly by the short-range packing interaction between water molecules. We also observe a strong linear correlation between the interfacial free energy and the melting temperature of different water models.