DEGAUSS-3p: A Three-Site Water Model from Soft Gaussian-Charge Electrostatics and a Rare-Gas-Informed Double-Exponential Potential

Abstract

Classical fixed-charge water models combine point-charge Coulomb interactions, which diverge at short distances and neglect charge penetration, with a Lennard–Jones 12–6 repulsion whose r–12 dependence does not reflect the near-exponential decay of quantum-mechanical exchange repulsion. The DEGAUSS force field replaces both with finite, Gaussian-smeared charge densities and a double-exponential van der Waals potential, with adjustable short-range softness and rare-gas-informed starting values for the double-exponential exponents. DEGAUSS-3p is parametrized directly for liquid water using these interaction forms. The resulting rigid three-site model captures the density anomaly and tetrahedral organization of liquid water, with a balanced description of structural, thermodynamic, and dynamic properties. Gaussian electrostatics and double-exponential repulsion thus provide an effective basis for modeling liquid water with finite interactions at short distances.