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Single-electron Fluorine Bonding. I. The SEFB-15 and CSFB-14 Benchmark Datasets, Reference Binding Energies and Intermolecular Bond Distances: Assessment of M06-2X density functional

  • Govinda Prasad Khanal
  • Elangannan Arunan
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Abstract

Halogen bonding in which a covalently bound fluorine acts as halogen-bond donor (F-bonding) is rare, and its open-shell variant with radical electron donors remains unexplored. We introduce SEFB-15 dataset (15 open-shell DF⋯CH3 complexes) exemplifying single-electron F-bonding (SEFB) and CSFB-14 dataset (14 closed-shell DF⋯NH3 complexes) representing closed-shell F-bonding (CSFB). Reference binding energies (BEs) at DF-RMP2-F12/CBS//DF-RMP2-F12/VDZ-F12 are validated against CCSD(T), CCSD(T)-F12b, W1-F12 and W2-F12 for selected systems (DF = F2, NCF, CNF, NH3F+ and NH2F2+), with MA%D of 4.5% (DF⋯CH3) and 3.4% (DF⋯NH3) against CCSD(T)-F12b/CBS//CCSD(T)-F12b/VDZ-F12. BEs from W1-F12 and W2-F12 are identical. Reference F-bond distances at DF-RMP2-F12/VDZ-F12 are validated against CCSD(T)-F12b, CCSD(T), CCSD, and DCSD for the same systems, with MA%D of 0.9% (SEFB) and 0.4% (CSFB) against CCSD(T)-F12b/VDZ-F12. M06-2X is recommended for closed-shell halogen bonding with heavier halogens but has never been assessed for open-shell F-bonding. M06-2X/AVTZ systematically overbinds all SEFB-15 complexes and underestimates their F-bond distances, with MA%Ds of 75.8% on BEs and 8.9% on F-bond distances. M06-2X predicts comparable BEs for F2⋯CH3 and F2⋯NH3, contrary to all ab initio results, an anomaly persisting across all 16 basis sets. Neither basis set nor BSSE correction resolves the overbinding. BSSE correction worsens BEs for DF⋯NH3 complexes. For CSFB-14, M06-2X/AVTZ yields MA%Ds of 16.0% for BEs and 3.3% for F-bond distances. M06-2X is reliable for CSFB but unreliable for SEFB regardless of basis set. Companion paper II reports performance of other Minnesota functionals and ab initio methods for these datasets.

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Cite

BibTeXRIS
BibTeX
@misc{khanal2026singleelectron,
  title = {{Single-electron Fluorine Bonding. I. The SEFB-15 and CSFB-14 Benchmark Datasets, Reference Binding Energies and Intermolecular Bond Distances: Assessment of M06-2X density functional}},
  author = {Govinda Prasad Khanal and Elangannan Arunan},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.16629},
  eprint = {2610.16629},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.16629},
}
RIS
TY  - UNPB
TI  - Single-electron Fluorine Bonding. I. The SEFB-15 and CSFB-14 Benchmark Datasets, Reference Binding Energies and Intermolecular Bond Distances: Assessment of M06-2X density functional
AU  - Govinda Prasad Khanal
AU  - Elangannan Arunan
PY  - 2026
DA  - 2026/10/12
PB  - arXiv
DO  - 10.48550/arxiv.2610.16629
UR  - https://arxiv.org/abs/2610.16629
AB  - Halogen bonding in which a covalently bound fluorine acts as halogen-bond donor (F-bonding) is rare, and its open-shell variant with radical electron donors remains unexplored. We introduce SEFB-15 dataset (15 open-shell DF⋯CH_3 complexes) exemplifying single-electron F-bonding (SEFB) and CSFB-14 dataset (14 closed-shell DF⋯NH_3 complexes) representing closed-shell F-bonding (CSFB). Reference binding energies (BEs) at DF-RMP2-F12/CBS//DF-RMP2-F12/VDZ-F12 are validated against CCSD(T), CCSD(T)-F12b, W1-F12 and W2-F12 for selected systems (DF = F_2, NCF, CNF, NH_3F^+ and NH_2F_2^+), with MA%D of 4.5% (DF⋯CH_3) and 3.4% (DF⋯NH_3) against CCSD(T)-F12b/CBS//CCSD(T)-F12b/VDZ-F12. BEs from W1-F12 and W2-F12 are identical. Reference F-bond distances at DF-RMP2-F12/VDZ-F12 are validated against CCSD(T)-F12b, CCSD(T), CCSD, and DCSD for the same systems, with MA%D of 0.9% (SEFB) and 0.4% (CSFB) against CCSD(T)-F12b/VDZ-F12. M06-2X is recommended for closed-shell halogen bonding with heavier halogens but has never been assessed for open-shell F-bonding. M06-2X/AVTZ systematically overbinds all SEFB-15 complexes and underestimates their F-bond distances, with MA%Ds of 75.8% on BEs and 8.9% on F-bond distances. M06-2X predicts comparable BEs for F_2⋯CH_3 and F_2⋯NH_3, contrary to all ab initio results, an anomaly persisting across all 16 basis sets. Neither basis set nor BSSE correction resolves the overbinding. BSSE correction worsens BEs for DF⋯NH_3 complexes. For CSFB-14, M06-2X/AVTZ yields MA%Ds of 16.0% for BEs and 3.3% for F-bond distances. M06-2X is reliable for CSFB but unreliable for SEFB regardless of basis set. Companion paper II reports performance of other Minnesota functionals and ab initio methods for these datasets.
ER  -