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Reassessing DFT Rankings for Ambimodal Cycloadditions: The Impact of Accurate CCSD(T) Benchmarks and New
Ruiqi Cong1, Rulin Feng1, Igor Ying Zhang1,2
1Research Center for Chemical Theory at Fudan, State Key Laboratory of Porous Materials for Separation and Conversion, Shanghai Key Laboratory of Molecular Catalysis and Innovation Materials, Collaborative Innovation Centre of Chemistry for Energy Materials, MOE Laboratory for Computational Physical Science, Department of Chemistry, Fudan University, Shanghai 200438, China.
None:
The accuracy of reference data is pivotal, especially when they are used to benchmark modern density functional approximations (DFAs) that approach chemical accuracy. This work re-examines a recent benchmark study on an ambimodal cycloaddition reaction. Using canonical coupled-cluster theory with single, double, and perturbative triple excitations [CCSD(T)] as a rigorous reference, we demonstrate that the performance ranking of leading DFAs is highly sensitive to the quality of the reference energies. Among the tested DFAs, the XYG3-type doubly hybrid (xDH) functional XYG7 emerges as the top performer against this robust benchmark. For strongly correlated subsets (GB1 > 12), CASPT2 is employed as a complementary reference to canonical CCSD(T). The renormalized doubly hybrid functional R-xDH7-SCC15 shows consistent performance across both reference frameworks. This cross-validation highlights the limitations of relying exclusively on single-reference benchmarks and underscores the urgent need for high-accuracy multireference reference data to properly evaluate next-generation density functionals.
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