Crash Rate as Function of Water Mass. First, we systematically determined the stability of time integration for TIP3P water models with modified masses of the oxygen atom (m O ) and hydrogen atoms (m H ). We varied the repartitioned mass m r from 0 to 8 g/mol in steps of 1 g/mol. For each repartitioning, we then varied the total mass in the regime of 0.5 < m tot < 1. / ns] Figure 2: Self-diffusion coefficient of neat TIP3P water at T = 310 K and p = 1 bar as a function of the mass repartitioning, m r . Diffusion coefficients are not corrected for finite-size effects. The total mass m tot of water molecules was unchanged. Data were averaged over two independent replicas, with differences between replicas being smaller than the symbol size. The line is a rational-function fit as guide to the eye. fluctuations in constant-pressure MD. To determine diffusion coefficients from the unwrapped trajectories, we used a generalized least-squares based estimator. We set the shortest lag time to 20 ps, resulting in excellent quality factors of the fits (Q ≈ 0.5). As we were only interested in relative changes due to m r and the system size was not varied, the values of the diffusion coefficients were not corrected for effects of finite system size, except if stated otherwise.