The Zeno (Z=1) behavior of water: A molecular simulation study

The regularity of fluid properties observed at the Zeno or Z = PV/RT = I po int has been proposed as a means of testing and improving Volumetric equati ons of state. Previous research has shown that molecular interactions can b e qualitatively and quantitatively related to the linear Z = 1 contour of T -r vs rho (r) for pure fluids from the Boyle temperature to the triple poin t. In this study, we expand the molecular simulation analysis of previous w ork to gain a detailed microscopic understanding of the properties of Zeno- point systems. Our calculations show that popular semiempirical water model s. such as SPC and SPC/E water, are able to replicate closely experimentall y determined water properties in the Zeno-paint region. Detailed molecular dynamics simulations of Z = 1.00 and adjacent Z = 0.75 and Z = 1.25 states reveal common features over a nide range of temperatures and densities, fro m 77 to 1097 degreesC and 1.01 to 0.029 g cm(-3). Radial distribution funct ions of high-temperature, high-density Zeno-point fluids display remarkable long-range structural correlation weil above the critical temperature and pressure, and examination of hydrogen bonding within each system shows that large water-water hydrogen-bonded clusters persist at high temperatures an d supercritical densities. These results are compared to the existing exten ded corresponding-states approaches for pure fluid properties.