Canonical and DLPNO-Based G4(MP2)XK-Inspired Composite Wave Function Methods Parametrized against Large and Chemically Diverse Training Sets: Are They More Accurate and/or Robust than Double-Hybrid DFT?

Emmanouil Semidalas,Jan M L Martin

doi:10.1021/acs.jctc.0c00189

Emmanouil Semidalas, Jan M L Martin

Open Access

https://doi.org/10.1021/acs.jctc.0c00189

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Abstract

The large and chemically diverse GMTKN55 benchmark was used as a training set for parametrizing composite wave function thermochemistry protocols akin to G4(MP2)XK theory (Chan, B.; Karton, A.; Raghavachari, K. J. Chem. Theory Comput. 2019, 15, 4478–4484). On account of their availability for elements H through Rn, Karlsruhe def2 basis sets were employed. Even after reparametrization, the GMTKN55 WTMAD2 (weighted mean absolute deviation, type 2) for G4(MP2)-XK is actually inferior to that of the best rung-4 DFT functional, ωB97M-V. By increasing the basis set for the MP2 part to def2-QZVPPD, we were able to substantially improve performance at modest cost (if an RI-MP2 approximation is made), with WTMAD2 for this G4(MP2)-XK-D method now comparable to the better rung-5 functionals (albeit at greater cost). A three-tier approach with a scaled MP3/def2-TZVPP intermediate step, however, leads to a G4(MP3)-D method that is markedly superior to even the best double hybrids ωB97M(2) and revDSD-PBEP86-D4. Evaluating the CCSD(T) component with a triple-ζ, rather than split-valence, basis set yields only a modest further improvement that is incommensurate with the drastic increase in computational cost. G4(MP3)-D and G4(MP2)-XK-D have about 40% better WTMAD2, at similar or lower computational cost, than their counterparts G4 and G4(MP2), respectively: detailed comparison reveals that the difference lies in larger molecules due to basis set incompleteness error. An E2/{T,Q} extrapolation and a CCSD(T)/def2-TZVP step provided the G4-T method of high accuracy and with just three fitted parameters. Using KS orbitals in MP2 leads to the G4(MP3|KS)-D method, which entirely eliminates the CCSD(T) step and has no steps costlier than scaled MP3; this shows a path forward to further improvements in double-hybrid density functional methods. None of our final selections require an empirical HLC correction; this cuts the number of empirical parameters in half and avoids discontinuities on potential energy surfaces. G4-T-DLPNO, a variant in which post-MP2 corrections are evaluated at the DLPNO-CCSD(T) level, achieves nearly the accuracy of G4-T but is applicable to much larger systems.

Highlights

Among applied computational chemists, density functional theory (DFT) is presently the most widely used electronic structure approach, followed by wave function ab initio theory (WFT)
Article with nearly 2500 main-group molecules, we found that the best DHDFT functionals, ωB97M(2) by Mardirossian and HeadGordon[49] and revDSD-PBEP86-D4 by our group,[45] have WTMAD2 statistics around 2.2 kcal/mol, competitive with or superior to the composite WFT (cWFT) methods we tested
Replacing def2-QZVPPD by an extrapolation E2/{T,Q} does not improve WTMAD2 and slightly raises it to 1.42 kcal/mol (G4-T-H6-v1)

Summary

Introduction

Density functional theory (DFT) is presently the most widely used electronic structure approach, followed by wave function ab initio theory (WFT). One well-established approach for reducing the computational cost of WFT methods has been the introduction of composite WFT (cWFT) protocols such as the following: Gaussian-n theory (Gn)[2−8] by the Pople group (see ref 9 for a review); The CBS-QB310,11 and related methods[12] by Petersson and co-workers; Multicoefficient correlation methods of Zhao and coworkers;[13−15] In a higher accuracy regime, the ccCA approach[16−18] of Wilson and co-workers; Received: February 25, 2020 Published: May 26, 2020.

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