An integral equation study of a simple point charge model of water

Abstract

We present an extensive integral equation study of a simple point charge model of water for a variety of thermodynamic states ranging from the vapor phase to the undercooled liquid. The calculations are carried out in the molecular reference-hypernetted chain approximation and the results are compared with extensive molecular dynamics simulations. Use of a hard sphere fluid as a reference system to provide the input reference bridge function leads to relatively good thermodynamics. However, at low temperatures the computed microscopic structure shows deficiencies that probably stem from the lack of orientational dependence in this bridge function. This is in marked contrast with results previously obtained for systems that, although similarly composed of angular triatomic molecules, do not tend to the tetrahedral coordinations that are characteristic of water.

Strategies to model the near‐solute solvent molecular density/polarization

“…5,6 Because the behavior of solute molecules in the absence of water may be totally different from that in the presence of water, the effect of water molecules should be included when studying biological problems such as protein folding and protein-protein/ligand interactions. [7][8][9][10] Solvent effects on biomolecules can be studied by several methods, 11,12 including molecular dynamics (MD) simulations, [13][14][15] Monte Carlo simulations, [16][17][18] integral equations, [19][20][21][22][23][24] and continuum dielectric methods. [25][26][27] Recently, the structure of solvent molecules near a solute has been incorporated in a set of microscopic electrodynamics equations, which mirror Maxwell's macroscopic electrodynamics equations, by using the solvent molecular density and orientation distributions to describe the distribution of the solvent molecules.…”

Effects of bridge functions on radial distribution functions of liquid water

“…This analytical approach often gives fair results on par with those by extensive Monte Carlo or molecular dynamics (MD) simulations, and combined with the reference interaction site model (RISM) method (Chandler and Andersen, 1972;Hansen and McDonald, 2006; Hirata and Rossky, 1981), can comprehensively describe the equilibrium properties of molecular liquids such as liquid water (Pettitt and Rossky, 1982), which plays essential roles in a variety of biochemical processes. Recent developments in the methods, algorithms and benchmarks (Lombardero et al, 1999;Lue and Blankschtein, 1995;Reddy et al, 2003;Richardi et al, 1999;Sato, 2013;Sumi and Sekino, 2006) indicate that the RISM-based integral equation approach can provide an alternative route for theoretical analyses on water and related aqueous systems with comparable reliability to more expensive, computer simulation approaches. However, it has also been observed (Lombardero et al, 1999;Lue and Blankschtein, 1995;Reddy et al, 2003;Richardi et al, 1999;Sato, 2013;Sumi and Sekino, 2006) that the descriptions of intermolecular correlations of water become less accurate at room temperature in comparison with at higher temperatures.…”

“…Recent developments in the methods, algorithms and benchmarks (Lombardero et al, 1999;Lue and Blankschtein, 1995;Reddy et al, 2003;Richardi et al, 1999;Sato, 2013;Sumi and Sekino, 2006) indicate that the RISM-based integral equation approach can provide an alternative route for theoretical analyses on water and related aqueous systems with comparable reliability to more expensive, computer simulation approaches. However, it has also been observed (Lombardero et al, 1999;Lue and Blankschtein, 1995;Reddy et al, 2003;Richardi et al, 1999;Sato, 2013;Sumi and Sekino, 2006) that the descriptions of intermolecular correlations of water become less accurate at room temperature in comparison with at higher temperatures.…”

The Importance of Excluded Solvent Volume Effects in Computing Hydration Free Energies

“…[7][8][9][10][11] Consequently, many methods have been developed for evaluating the solvation free energy, including free-energy simulations, [12][13][14][15][16][17][18] Monte Carlo simulations, 4,[19][20][21][22] integral equations, [22][23][24][25][26][27][28][29] solvent-accessible surface area calculations, [30][31][32][33][34][35] and continuum dielectric methods. [36][37][38][39][40] The latter, including the Born equation, 41 the generalized Born equation, 33,[42][43][44][45][46] and the Poisson equation, 47 have been widely used to compute the electrostatic component of the solvation free energy, ∆G solv elec , because they are less costly compared to simulations including explicit solvent molecules.…”