The self-diffusion coefficient of water shows an anomalous increase with increasing hydrostatic pressure up to a broad maximum (P-mD) near 1 kbar at 298 K, which has been attributed to pressure effects on the tetrahedral hydrogen bond network of water. Moreover, the ability of a water model to reproduce anomalous properties of water is a signature that it is reproducing the network. Here, water was simulated between 1 bar and 5 kbar using three water models, two four-site (with all charges in the molecular plane) and one single-site multipole (which accounts for out-of-molecular plane charge), that have reasonable pressure-temperature properties. For these three models, the diffusion coefficients display a maximum in the pressure dependence and the radial distribution functions show good agreement with the limited experimental structural data at high pressure that are available. In addition, a variety of properties associated with the network are examined, including hydrogen bond lifetimes and occupancies, three-body angle distributions, and tetrahedral order parameters. Results suggest that the initial increasing diffusion with pressure is because hydrogen bonds are distorted and thus weakened by pressure, but above P-mD, the hydrogen bonds are weakened to the point it behaves more like a normal liquid. In other words, the P-mD may be a measure of the angular strength of hydrogen bonds. In addition, since the four-site models over-predict the values of P-mD while the multipole model under-predicts it, out-of-plane charge may improve four-site models.
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