Simulation of the Interaction Potential between Water Molecules

Abstract

The structure and the explicit form of the interaction potential between molecules in water vapor have been studied. The main contribution to this potential is supposed to be made by repulsive, dispersion, and electrostatic forces. The irreducible contribution caused by the overlapping of the electron shells of water molecules, which is usually associated with hydrogen bonds, is supposed to be small and neglected. Interaction potentials, in which the molecular repulsion is described by either a "soft" power-law potential or a hard-core one, have been constructed. In both cases, a multipole series expansion up to the dipole-octupole term is used for the electrostatic interaction between molecules. The dispersion interaction is approximated by the standard London formula. The multipole moments are taken to be equal to their experimental values or close to their values obtained from quantum chemical calculations. The model parameters for the repulsive and dispersion potentials are selected to correctly reproduce the parameters of an isolated dimer and the temperature dependence of the second virial coefficient. The obtained potentials are used to construct the average potentials of interaction between the molecules, which govern the thermodynamic, kinetic, and electrophysical properties of water vapor. A characteristic feature of the repulsive potential is the value of power exponent: = 28. The proposed potentials differ substantially from the well-known ones, such as SPC, SPC/E, TIPS, and other potentials. K e y w o r d s: water vapor, molecular interaction potential.

Modelling of potentials for interparticle interactions between methanol molecules

“…Rigorously speaking, these potentials are only correct for a vapor phase, where the screening effect can be ignored. In order to build them we have used an approach similar to that for the water potential [15]. It is shown that the averaged potential can be approximated by the expression, whose structure is close to the one for the Lennard-Jones potential.…”

“…H-bonds are considered as a sum of electrostatic interaction and an irreducible one caused by exchange effects arising due to the overlapping of the electronic shells of molecules. It was shown in many works [10][11][12][13][14][15] that H-bond in water is mainly of electrostatic nature. The irreducible part of H-bond, caused by the overlapping of electron shells and corresponding exchange effects, does not exceed 10−15% [14].…”

“…However, the intermediate application of (4.3) to water, methanol and other alcohols is impossible since their interparticle potentials have a more complex structure (see [1,28,29]). In this case, it is necessary to pay attention to the fact that thermodynamic properties of low-molecular liquids with nonspherical particles are determined by the averaged potentials having the structure (4.4) (see details in [15,22]). Thereto, the averaged potentials are not fully equivalent to (4.4) since their parameters ε a and σ a depend on temperature.…”

Dimerization Degree of Water Molecules, Their Effective Polarizability, and Heat Capacity of Saturated Water Vapor

“…5. Зазначимо, що ефекти екранування враховую-ться тiльки для мультипольних потенцiалiв (МП) [29]. Параметри потенцiалу Ленард-Джонса, що вiдповiдають диполь-дипольнiй взаємодiї двох ди-мерiв, визначенi в Додатку.…”

“…Звернемо увагу на те, що числовi значення˜( a) m ( ) i m ( ) для SPC-потенцiалу, що розраховуються у [22,29,31], залежать вiд температури (див. рис.…”