Atom-Bond Electronegativity Equalization Method Fused into Molecular Mechanics. II. A Seven-Site Fluctuating Charge and Flexible Body Water Potential Function for Liquid Water

Abstract

The ABEEM-7P model, which is a transferable, intermolecular-potential seven-points approach including fluctuating charges and flexible body, is based on the combination of the atom-bond electronegativity equalization (ABEEM) and molecular mechanics (MM). This model has been successfully explored in regard to the properties of gas-phase small water clusters in reasonable agreement with available experiments and other water models. This model is further tested by comparing the calculated energetic, structural, and dynamic properties of liquid water over a range of temperatures (260−348 K) with available experimental results and those from other water models. Molecular dynamics simulations of liquid water with ABEEM-7P were performed using the Tinker MM program. All simulations were conducted in the microcanonical NVE ensemble or canonical NVT ensemble, using 216 water molecules in a cubic simulation cell furnished with periodic boundary and minimum image conditions, and the density of the solvent was set to the experimental value for the temperature of interest. The ABEEM-7P potential gives a reasonable experimental reproduction of the intramolecular O−H bond length and H−O−H bond angle in the liquid at room temperature. The ABEEM-7P model presents the quantitative charges of O atoms, H atoms, O−H bonds, and lone-pair electrons per monomer water in the liquid and their changing in response to different ambient environment from 260 K to 348 K. Especially, ABEEM-7P applies the parameter klp,H(Rlp,H) to explicitly describe short-range interaction of the hydrogen bond in the hydrogen-bond interaction region. The computed ABEEM-7P properties of the liquid-phase water at room temperature, such as average dipole moment, static dielectric constant, heats of vaporization, radial distribution function, and diffusion constant, are fairly consistent with the available experimental results. The ABEEM-7P model also performs well for the temperature dependence of liquid properties: the static dielectric constant and the heats of vaporization by ABEEM-7P decrease as the temperature increases, in good agreement with the experimental values.