The Yukagua model of water

Using the Invariant Expansion technique we show that the Multi-Yukawa closu re of the Ornstein Zernike equation has an analytical solution for a model that reproduces well the known structure of water as measured by neutron di ffraction. The model is an extension of earlier models based on the BBL mod el [1,2]: the analytical sticky octupolar potential and the soft version of that potential. In the present work the soft short-ranged effective potent ial is represented by a sum of Yukawa potentials. The models is tested by M onte Carlo Computer simulation. The atom-atom pair correlation functions fo r oxygen-oxygen, oxygen-hydrogen and hydrogen hydrogen obtained for this ne w potential are in good agreement with the neutron scattering experiments. Because of its analyticity this model is especially suited for the investig ation of the percolation transition for the hydrogen bonds, proposed by Sta nley and collaborators [3,4,39,40]. The convergence in the simulations is v ery fast because the weakly directional octupolar potential have little tro uble connecting to the tetrahedral first nearest neighbors. The observation made in the computer simulations is that small changes in the strength of the potential seem to lock in or lock out of the tetrahedral structure. Thi s is interpreted as changes in temperature producing the percolation transi tion. (C) 1999 Elsevier Science B.V. All rights reserved.