Tests of the DFT Ladder for the Fulminic Acid Challenge
Ashley M Allen1, Laura N Olive Dornshuld1, Patricia A Gonzalez Franco1
1Center for Computational Quantum Chemistry, University of Georgia, Athens, Georgia 30602, United States.
Journal of the American Chemical Society
|April 16, 2025
Summary
Density functional theory (DFT) struggles to accurately predict properties of the challenging fulminic acid (HCNO) molecule. Different DFT functionals yield conflicting results for its geometry and electronic structure, indicating a lack of consensus.
Area of Science:
- Computational Chemistry
- Quantum Chemistry
- Theoretical Chemistry
Background:
- Fulminic acid (HCNO) is a historically significant molecule with unique chemical properties.
- Density functional theory (DFT) is a widely used computational method for predicting molecular properties.
Purpose of the Study:
- To evaluate the performance of a wide range of contemporary DFT functionals for the challenging HCNO molecule.
- To analyze the accuracy of DFT for predicting geometric parameters, vibrational frequencies, and reaction energies of HCNO.
- To investigate the impact of dispersion corrections on HCNO properties.
Main Methods:
- Computation of molecular properties using 473 different DFT functionals.
- Statistical analysis of geometric parameters, vibrational frequencies, barriers to linearity, and dissociation energy.
- Assessment of the "DFT ladder" for convergence towards accurate predictions.
Main Results:
- No clear consensus or consistent improvement in accuracy was observed as DFT functionals of higher "rungs" were used.
- High-ranking DFT functionals showed better performance for the reaction energy, while lower-ranking functionals were better for bond distances and frequencies.
- Dispersion corrections had significant side effects on covalently bonded properties and thermochemistry.
Conclusions:
- The current collection of DFT approximations does not provide a reliable, transparent progression towards accurate predictions for HCNO.
- DFT performance for HCNO is highly dependent on the specific functional and property being investigated.
- Further development of DFT methods is needed for accurately describing challenging chemical systems like fulminic acid.
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