A modified TIP3P water potential for simulation with Ewald summation

TLDR

The authors modified the TIP3P water potential’s charges and Lennard‑Jones parameters to enhance performance with Ewald summation in molecular dynamics simulations. They optimized the TIP3P parameters by removing hydrogen Lennard‑Jones terms, making the model rule‑independent, and explored additional models—including a long‑range correction for truncated Lennard‑Jones interactions—to improve accuracy. The modified model reproduces experimental density, heat of vaporization, and diffusion, improves the O–O radial distribution and dielectric constant, yet still lacks a temperature density maximum, and the long‑range correction only marginally refines the dielectric constant.

Abstract

The charges and Lennard-Jones parameters of the TIP3P water potential have been modified to improve its performance under the common condition for molecular dynamics simulations of using Ewald summation in lieu of relatively short nonbonded truncation schemes. These parameters were optimized under the condition that the hydrogen atoms do not have Lennard-Jones parameters, thus making the model independent of the combining rules used for the calculation of nonbonded, heteroatomic interaction energies, and limiting the number of Lennard-Jones calculations required. Under these conditions, this model provides accurate density (ρ=0.997 g/ml) and heat of vaporization (ΔHvap=10.53 kcal/mol) at 25 °C and 1 atm, but also provides improved structure in the second peak of the O–O radial distribution function and improved values for the dielectric constant (ε0=89) and the diffusion coefficient (D=4.0×10−5 cm2/s) relative to the original parametrization. Like the original parameterization, however, this model does not show a temperature density maximum. Several similar models are considered with the additional constraint of trying to match the performance of the optimized potentials for liquid simulation atom force field to that obtained when using the simulation conditions under which it was originally designed, but no model was entirely satisfactory in reproducing the relative difference in free energies of hydration between the model compounds, phenol and benzene. Finally, a model that incorporates a long-range correction for truncated Lennard-Jones interactions is presented, which provides a very accurate dielectric constant (ε0=76), however, the improvement in this estimate is on the same order as the uncertainty in the calculation.