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Delocalization error poisons the density-functional many-body expansion
Dustin R Broderick1, John M Herbert1
1Department of Chemistry & Biochemistry, The Ohio State University 151 W. Woodruff Ave. Columbus Ohio 43210 USA herbert@chemistry.ohio-state.edu.
Chemical Science
|November 21, 2024
Summary
The many-body expansion combined with density functional theory shows significant errors in ion-water interactions due to self-interaction errors. Energy-based screening can mitigate these issues, but caution is advised for this quantum chemistry method.
Area of Science:
- Computational Chemistry
- Quantum Chemistry
- Physical Chemistry
Background:
- The many-body expansion (MBE) is a fragment-based method for large-scale quantum chemistry calculations.
- MBE is increasingly used for fitting force fields and in machine learning, particularly for water and aqueous systems.
- Previous studies have not highlighted significant issues with MBE in these contexts.
Purpose of the Study:
- To investigate the accuracy and limitations of the many-body expansion when combined with semilocal density functional theory for ion-water interactions.
- To identify the source of errors and explore potential mitigation strategies.
Main Methods:
- Utilized the many-body expansion approach with semilocal density functional theory (DFT).
- Examined ion-water interactions, specifically F-(H2O)N clusters with N >= 15.
- Tested various mitigation strategies including hybrid functionals, counterpoise correction, density correction, and dielectric continuum models.
- Investigated energy-based screening as a potential solution.
Main Results:
- Semilocal DFT combined with MBE exhibits wild oscillations and error accumulation in ion-water interactions for clusters N >= 15.
- Self-interaction error in DFT is identified as the primary cause of these divergent behaviors.
- The errors are minor in small clusters but become catastrophic in larger ones.
- Hybrid functionals with >50% exact exchange can counteract errors, but modern meta-GGAs (ωB97X-V, SCAN, SCAN0) are insufficient.
- Counterpoise correction, density correction, and continuum models show limited effectiveness.
- Energy-based screening successfully prevents divergent behavior.
Conclusions:
- Extreme caution is necessary when using the many-body expansion with density functional theory for ion-water systems.
- Self-interaction error is a critical issue that can lead to catastrophic failures in MBE-DFT calculations.
- Energy-based screening offers a viable strategy to improve the reliability of MBE-DFT for such systems.
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