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A new analytic equation of state for liquid water C. A. Jeffery and P. H. Austina)

Summary: A new analytic equation of state for liquid water
C. A. Jeffery and P. H. Austina)
Atmospheric Sciences Programme, #217 Geography, 1984 West Mall, University of British Columbia,
Vancouver, British Columbia V6T 1Z2, Canada
Received 20 May 1998; accepted 1 October 1998
We develop a new analytical equation of state for water based on the Song, Mason, and Ihm
equation of state and Poole et al.'s simple model of the free energy of strong tetrahedral hydrogen
bonds. Repulsive and attractive forces are modeled using a modification of the Weeks­Chandler­
Anderson decomposition of the pair potential, with closed tetrahedral hydrogen bonds contributing
both internal energy and entropy to the free energy of water. Strong tetrahedral hydrogen bonds are
modeled explicitly using a simplified partition function. The resulting equation of state is 20­30
times more accurate than equivalent simple cubic equations of state over a wide range of pressures
0.13000 bar and temperatures 341200 °C including the supercooled region. The new
equation of state predicts a second liquid­liquid critical point at pC 0.954 kbar, C
1.045 g cm 3
and TC 228.3 K. The temperature of this second critical point is above the
homogeneous freezing temperature at 1 kbar, thus this region of the phase diagram may be
experimentally accessible. The phase diagram also suggests that the homogeneous nucleation
temperature above 1.2 kbar may be determined by a phase transition from high-density water to
low-density water. © 1999 American Institute of Physics. S0021-9606 99 52701-3


Source: Austin, Philip H. - Department of Earth and Ocean Sciences, University of British Columbia


Collections: Geosciences