Abstract
Using the large and chemically diverse GMTKN55 dataset, we have tested the performance of pure and hybrid KS-DFT and HF-DFT functionals constructed from three variants of the SCAN meta-GGA exchange-correlation functional: original SCAN, rSCAN, and r2SCAN. Without any dispersion correction involved, HF-SCANn outperforms the two other HF-DFT functionals. In contrast, among the self-consistent variants, SCANn and r2SCANn offer essentially the same performance at lower percentages of HF-exchange, while at higher percentages, SCANn marginally outperforms r2SCANn and rSCANn. However, with D4 dispersion correction included, all three HF-DFT-D4 variants perform similarly, and among the self-consistent counterparts, r2SCANn-D4 outperforms the other two variants across the board. In view of the much milder grid dependence of r2SCAN vs. SCAN, r2SCAN is to be preferred across the board, also in HF-DFT and hybrid KS-DFT contexts.
Highlights
In 2001, the “Jacob’s Ladder” was proposed [1] as an organizing principle for the DFT “functional zoo”
For the functionals, we have used the same terminology we proposed in [29] for different GGAs and mGGAs—HF-SCANn, HF-rSCANn, and HF-r2SCANn for the HF-DFT series and SCANn, rSCANn, and r2SCANn for the corresponding self-consistent counterparts, where n is the percentage of HF exchange (HFx) used for the hybrid form, and it ranges from 0–50%
Identical to the self-consistent SCANn [29], the overall WTMAD2 minimum is near 30% HFx for both the rSCANn and r2SCANn
Summary
In 2001, the “Jacob’s Ladder” was proposed [1] as an organizing principle for the DFT “functional zoo”. Rung one is the LDA [2] (local density approximation, exact for a uniform electron gas). Rung two (GGA or generalized gradient approximation) adds the reduced density gradient (see [3,4,5,6] and references therein). The great improvement in performance of GGA over LDA marked a turning point in the acceptance of DFT as a molecular modeling technique. To satisfy additional constraints, one needs to climb up the Jacob’s Ladder to rung three, mGGAs (meta-GGAs, where either the Laplacian or the kinetic energy density are included). In 2015, Sun et al [10] first succeeded in satisfying all 17 constraints with the nonempirical SCAN (strongly constrained and appropriately normed) mGGA functional. Several studies have proven SCAN’s broad transferability [11] as well as improved DFT description for different systems, such as metal oxides [12], energetics and structures of different ice and silicon phases [11], high-temperature superconductors [13], liquid, water, and ice [14], and so on
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