Toward Accuracy and Efficiency: A Polarizable Bond-Dipole-Based Water Model.

Abstract

A polarizable water model, PBFF-WAT-2025, is developed on the basis of chemical bond dipoles as the fundamental electrostatic sites. In this framework, both permanent and induced dipole contributions are assigned to each bond dipole, providing a physically motivated alternative to atom-centered multipole schemes. For computational efficiency, the induced dipole vectors are constrained to be collinear with the corresponding permanent dipoles. The potential loss of angular flexibility is compensated by the inclusion of orbital-interaction terms, through which the directionality of hydrogen bonding and the essential anisotropy in the electrostatics are incorporated. The accuracy of the model is assessed against CCSD(T) reference data for water clusters, yielding root-mean-square deviations of 1.39 kcal/mol for total interaction energies and 1.10 kcal/mol for three-body contributions. Thermodynamic and dynamic properties of bulk water, including density, enthalpy of vaporization, thermal expansion coefficient, isobaric heat capacity, isothermal compressibility, self-diffusion coefficient, and average dipole moment, are evaluated and shown to be in reasonable agreement with experiment. Although polarization is explicitly treated, computational overhead is minimized by the robustness of the bond-dipole representation, which allows dipole updates to be performed infrequently during molecular dynamics simulations. By balancing physical fidelity with efficiency, the PBFF-WAT-2025 model is demonstrated to provide a transferable and computationally practical framework for long-time scale and large-system simulations of aqueous and biomolecular systems.