Orbital-Optimized Density Functional Calculations Improve Dipole Moment Predictions for Rydberg States
Researchers used orbital-optimized density functional theory (DFT) with a plane waves basis set to compute dipole moments of multiple Rydberg excited states across a set of molecules. Rydberg states are notoriously difficult to model due to their highly diffuse electron density, and prior benchmarks of orbital-optimized DFT had focused almost exclusively on excitation energies rather than dipole moments. The findings reveal significant limitations in commonly used atomic orbital basis sets and provide guidance on which DFT functionals perform best for these challenging states.
A new preprint posted to arXiv investigates the accuracy of orbital-optimized density functional calculations for predicting dipole moments of Rydberg excited states, going beyond the excitation energies that have dominated prior benchmarks. The study employs a plane waves basis set, which offers a more flexible representation of the highly diffuse Rydberg orbitals compared to conventional atomic orbital basis sets. A key finding is that single-augmented atomic basis sets yield inaccurate dipole moments even when excitation energies appear converged, and discrepancies with plane waves results persist for the most diffuse states even after adding extra diffuse augmentation functions. Among the functionals tested, the generalized gradient approximation functional PBE showed good agreement with higher-level reference calculations, and the hybrid functional PBE0 further improved results. By contrast, PBE with a globally scaled explicit Perdew-Zunger self-interaction correction produced larger errors and systematically overestimated dipole moments, despite correctly restoring the asymptotic −1/r behavior of the Kohn-Sham potential. The work highlights that basis set choice is a critical and underappreciated source of error when computing excited-state properties beyond excitation energies.
What's missing
The benchmark set of molecules is not specified in the abstract, so the generalizability of the findings to a broader chemical space is unclear. The paper does not address computational cost trade-offs between plane waves and augmented atomic basis sets, which is relevant for practical applications to larger systems.
What different sources said
- arXiv physicsCenter
Excited-state Properties Beyond the Excitation Energy from Orbital-Optimized Density Functional Calculations I: Dipole Moments of Rydberg States
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