Application of the reference interaction site model theory to analysis on surface-induced structure of water

We consider the extended simple point charge (SPC/E) model water near uncharged and charged macroparticles. It is shown that the size of the macroparticle tested is sufficiently large and it acts in effect as a planar wall. The reference interaction site model (RISM) theory is employed, and a robust and very efficient algorithm has been developed for solving the basic equations. The algorithm is a hybrid of the Picard and Newton-Raphson methods. The Jacobian matrix is just part of the input data and need not be recalculated at all. Sufficiently accurate solutions are obtained in only 7 to 16 iterations. The reduced density profile of oxygen atoms near an uncharged macroparticle indicates significant dewetting and a clear contribution of the icelike structure. The surface potential calculated is positive but very small. When the macroparticle is charged, the number of water molecules in the close vicinity of the surface increases regardless of the sign of the charge. The interaction between uncharged macroparticles with sufficiently large sizes immersed in pure water is attractive and very strong at small separations. The interaction between negatively charged macroparticles is ''more repulsive'' than between positively charged macroparticles. On the whole, however, the asymmetry of the SPC/E water in responding to positively and negatively charged surfaces is not high. It has been shown that the results obtained from the RISM theory combined with the SPC/E water are in qualitative accord with those calculated by the reference hypernetted-chain (RHNC) theory for hard spheres with embedded dipoles and tetrahedral quadrupoles, in terms of reduced density profiles, surface potential, and macroparticle interactions. (C) 1996 American Institute of Physics.