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More Converged, Less Accurate? Reassessing Ab Initio Water Simulation Standards

Computational chemists assumed that increasing basis set sizes and convergence criteria in electronic structure theory guaranteed more realistic liquid water simulations; unmasking cancellation-of-error artifacts shows standard approximations break down in condensed phases.

Author
Hubert Beck et al.
Published
2026
Journal
The Journal of Physical Chemistry B
Last updated
September 2026
More Converged, Less Accurate? Reassessing Ab Initio Water Simulation Standards

Liquid water is the universal solvent of biological life, yet accurately modeling its anomalous density, hydrogen-bonding networks, and dielectric properties using first-principles quantum mechanics remains notoriously difficult.

For decades, simulation protocols relied on an implicit assumption: systematically tightening numerical basis set limits and energy convergence thresholds would steadily yield better agreement with real-world water experiments.

This provocative Journal of Physical Chemistry B investigation demonstrates a shocking paradox: increasing computational convergence often degrades simulation accuracy because uncorrected nuclear quantum effects and many-body dispersion forces were historically masked by fortuitous cancellations of error in lower-tier calculations.

This critical finding forces a wholesale re-evaluation of ab initio molecular dynamics protocols, paving the way for machine-learned many-body potential surfaces that accurately capture water's liquid dynamics across biophysics and climate modeling.

Reference

Beck, H., & Marsalek, O. (2026). More Converged, Less Accurate? Reassessing Standard Choices for Ab Initio Water Using Machine Learning Potentials. The Journal of Physical Chemistry B, 130(28), 7215–7226.

Title

More Converged, Less Accurate? Reassessing Standard Choices for Ab Initio Water Using Machine Learning Potentials

Abstract

Accurately simulating the properties of liquid water remains a central challenge in molecular simulations. In this work, we use machine learning potentials to investigate how the convergence settings of electronic structure calculations impact the predicted structural and dynamical properties of simulated water and ice. We evaluate the true performance of several reference methods in classical and path-integral molecular dynamics. When we compare a popular, computationally pragmatic revPBE0-D3 setup against a highly converged one, our results reveal that its widely reported experimental agreement degrades. Applying the same highly converged settings to the ωB97X-rV functional, we find an improved agreement with experimental results. MP2 with a triple-ζ basis set, commonly used for liquid water, shows poor performance, which is indicative of insufficient convergence. These findings underscore the need for fully converged reference calculations when evaluating the fundamental accuracy of electronic structure methods and developing reliable models for aqueous systems.

Cited 1 times · View on doi.org

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