Simple Modifications of the SCAN Meta-Generalized Gradient Approximation Functional

Abstract

We analyzed various possibilities to improve upon the SCAN meta-generalized gradient approximation density functional obeying all known properties of the exact functional that can be satisfied at this level of approximation. We examined the necessity of locally satisfying a strongly tightened lower bound for the exchange energy density in single-orbital regions, the nature of the error cancellation between the exchange and correlation parts in two-electron regions, and the effect of the fourth-order term in the gradient expansion of the correlation energy density. We have concluded that the functional can be modified to separately reproduce the exchange and correlation energies of the helium atom by locally releasing the strongly tightened lower bound for the exchange energy density in single-orbital regions, but this leads to an unbalanced improvement in the single-orbital electron densities. Therefore, we decided to keep the F ≤ 1.174 exact condition for any single-orbital density, where F is the exchange enhancement factor. However, we observed a general improvement in the single-orbital electron densities by revising the correlation functional form to follow the second-order gradient expansion in a wider range. Our new revSCAN functional provides more-accurate atomization energies for the systems with multireference character, compared to the SCAN functional. The nonlocal VV10 dispersion-corrected revSCAN functional yields more-accurate noncovalent interaction energies than the VV10-corrected SCAN functional. Furthermore, its global hybrid version with 25% of exact exchange, called revSCAN0, generally performs better than the similar SCAN0 for reaction barrier heights. Here, we also analyzed the possibility of the construction of a local hybrid from the SCAN exchange and a specific locally bounded nonconventional exact exchange energy density. We predict compatibility problems since this nonconventional exact exchange energy density does not really obey the strongly tightened lower bound for the exchange energy density in single-orbital regions.

First-Principles Calculation of Transition Metal Hyperfine Coupling Constants with the Strongly Constrained and Appropriately Normed (SCAN) Density Functional and its Hybrid Variants

“…The SCAN functional has inspired a series of recent studies that investigated the definition of simple hybrid as well as double-hybrid functionals using SCAN as the basic mGGA component [28,29,31]. As an example, SCAN0 [29], a hybrid with 25% exact exchange, has been reported to offer improved performance for a variety of properties, including reaction energetics of late transition metal systems [31].…”

“…Studies that examined the performance of SCAN and certain derivative functionals have already indicated that it performs well for a variety of energy-related properties, usually surpassing previous GGA and mGGA approaches [22][23][24][25][26][27][28][29][30][31]. However, it is unclear whether these advances also translate into improved description of the physical mechanisms that give rise to the distinct contributions to hyperfine coupling.…”

Performance of the DLPNO-CCSD and recent DFT methods in the calculation of isotropic and dipolar contributions to 14N hyperfine coupling constants of nitroxide radicals

“…14 N HFCC were calculated using some newer density functionals available in Libxc [23]. DFT functionals used are: strongly constrained and appropriately normed semilocal density functional (SCAN) [24] (we didn't nd signi cant differences between the results of SCAN and revised SCAN functional [25] hence the results of the calculations using the latter are not presented), hybrid SCAN0 [26] (also similar to the results of the revised version), bayesian error estimation functional (BEEF) [27], power series extension of the PBE exchange functional [28] (PBEpow exchange functional combined with the PBE [29] correlation functional), PBE-GX functional [30] (combined with the PBE correlation functional), MN15 and MN15-L functionals [31,32], PBE1KCIS hybrid [33] (with KCIS correlation functional [34]), screened Coulomb potential hybrid functional (HSE06) [35] and B98 hybrid [36]. We compared these functionals with the functionals used in our previous paper [6]: GGA functionals BP86 [37,38], PBE [29], OLYP [39]; the meta-GGA functionals TPSS [40], M06L [41]; the hybrid GGA functionals B3LYP [42], PBE0 [43], mPW1PW [44], B97 [45], BHandHLYP [46]; the hybrid meta-GGA functionals TPSS0 [40], M06 [47], M06-2X [47]; the range-separated functionals CAM-B3LYP [48], ωB97x [49], the double-hybrid functional B2PLYP (with relaxed density) [50].…”

New Light on an Old Story: Breaking Kasha’s Rule in Phosphorescence Mechanism of Organic Boron Compounds and Molecule Design

“…Vibrational frequencies were also calculated after optimization to ensure that these structures are stable points. To find a suitable XC functional, a series of XC functionals have been examined combined with the basis set 6-311G(d,p) [ 29 , 30 ], including BLYP [ 31 , 32 ], B3LYP [ 33 , 34 ], PBE0 [ 35 , 36 ], CAM-B3LYP [ 37 ], B97XD [ 38 ], recently developed SCAN0 [ 39 , 40 , 41 ], and so on (see the Supplementary Materials ). The experimental spectra of S-BF2 were measured in dichloromethane (CH 2 Cl 2 ), so the solvent environment was implicitly simulated by the polarizable continuum model (PCM) [ 42 ].…”