DEGAUSS: A Novel Softcore Force Field Using Double Exponential van der Waals and Gaussian Charge for Molecular Dynamics Simulations I: Theory and Validation

Classical molecular force fields contain singularities in Lennard-Jones and Coulombic potentials that cause numerical challenges under extreme conditions, including transition states, high temperatures and pressures, and alchemical free energy calculations. We present DEGAUSS, a singularity-free force field framework that eliminates these divergences by replacing Lennard-Jones potentials with double exponential functions and point charges with Gaussian charge distributions, ensuring that all interactions remain finite even at zero separation. Using existing classical force field parameters as a starting point, we define DEGAUSS-specific parameters that closely resemble the behaviors of the classical force field, while avoiding numerical instabilities. Validation studies of TIP3P and OPC3 water models demonstrate excellent reproduction of thermodynamic and structural properties across diverse temperature ranges. Alanine dipeptide simulations preserve major conformational states, and protein benchmarks show structural stability consistent with that of conventional force fields. Hydration free energy calculations using alchemical methods demonstrate the absence of singularities during particle annihilation without requiring additional softcore potentials while producing results comparable to classical methods. Although the smooth functional forms increase computational costs relative to standard Lennard-Jones potentials and Coulomb potentials, DEGAUSS provides a robust framework that maintains chemical accuracy and simplifies alchemical free energy calculations.