Does Basis Set Superposition Error Significantly Affect Post-CCSD(T) Corrections?

We have investigated the title question for both a subset of the W4-11 total atomization energies benchmark, and for the A24x8 noncovalent interactions benchmark. Overall, counterpoise corrections to post-CCSD(T) contributions are about two orders of magnitude less important than those to the CCSD(T) interaction energy. Counterpoise corrections for connected quadruple substitutions (Q) are negligible, and or especially so.

Basis Set Extrapolation from the Vanishing Counterpoise Correction Condition.

Basis set extrapolations are typically rationalized either from analytical arguments involving the partial-wave or principal expansions of the correlation energy in helium-like systems or from fitting extrapolation parameters to reference energetics for a small(ish) training set. Seeking to avoid both, we explore a third alternative: extracting extrapolation parameters from the requirement that the BSSE (basis set superposition error) should vanish at the complete basis set limit. We find this to be a viable approach provided that the underlying basis sets are not too small and reasonably well balanced.

W4Λ: Leveraging Λ Coupled-Cluster for Accurate Computational Thermochemistry Approaches.

High-accuracy composite wave function methods like Weizmann-4 (W4) theory, high-accuracy extrapolated ab initio thermochemistry (HEAT), and the Feller-Peterson-Dixon (FPD) approach enable sub-kJ/mol accuracy in gas-phase thermochemical properties. Their biggest computational bottleneck is the evaluation of the valence post-CCSD(T) correction term. We demonstrate here, for the W4-17 thermochemistry benchmark and subsets thereof, that the Λ coupled-cluster expansion converges more rapidly and smoothly than the regular coupled-cluster series.

Correlation Consistent Basis Sets for Explicitly Correlated Theory: The Transition Metals.

We present correlation consistent basis sets for explicitly correlated (F12) calculations, denoted VZ(-PP)-F12-wis ( = D,T), for the -block elements. The cc-pVDZ-F12-wis basis set is contracted to [8s7p5d2f] for the 3-block, while its ECP counterpart for the 4 and 5-blocks, cc-pVDZ-PP-F12-wis, is contracted to [6s6p5d2f]. The corresponding contracted sizes for cc-pVTZ(-PP)-F12-wis are [98632] for the 3-block elements and [77632] for the 4 and 5-block elements.

S66x8 noncovalent interactions revisited: new benchmark and performance of composite localized coupled-cluster methods.

The S66x8 noncovalent interactions benchmark has been re-evaluated at the "sterling silver" level, using explicitly correlated MP2-F12 near the complete basis set limit, CCSD(F12*)/aug-cc-pVTZ-F12, and a (T) correction from conventional CCSD(T)/sano-V{D,T}Z+ calculations. The revised reference values differ by 0.1 kcal mol RMS from the original Hobza benchmark and its revision by Brauer , but by only 0.

Automatic generation of complementary auxiliary basis sets for explicitly correlated methods.

Explicitly correlated calculations, aside from the orbital basis set, typically require three auxiliary basis sets: Coulomb-exchange fitting (JK), resolution of the identity MP2 (RI-MP2), and complementary auxiliary basis set (CABS). If unavailable for the orbital basis set and chemical elements of interest, the first two can be auto-generated on the fly using existing algorithms, but not the third. In this paper, we present a quite simple algorithm named autoCABS; a Python implementation under a free software license is offered at Github.

The MOBH35 Metal-Organic Barrier Heights Reconsidered: Performance of Local-Orbital Coupled Cluster Approaches in Different Static Correlation Regimes.

We have revisited the MOBH35 (Metal-Organic Barrier Heights, 35 reactions) benchmark [Iron; , Janes, , 2019, 123 (17), 3761-3781; ibid. 2019, 123, 6379-6380] for realistic organometallic catalytic reactions, using both canonical CCSD(T) and localized orbital approximations to it. For low levels of static correlation, all of DLPNO-CCSD(T), PNO-LCCSD(T), and LNO-CCSD(T) perform well; for moderately strong levels of static correlation, DLPNO-CCSD(T) and (T) may break down catastrophically, and PNO-LCCSD(T) is vulnerable as well.

Surprisingly Good Performance of XYG3 Family Functionals Using a Scaled KS-MP3 Correlation.

By adding a GLPT3 (third-order Görling-Levy perturbation theory, or KS-MP3) term to the XYG7 form for a double hybrid, we are able to bring down WTMAD2 (weighted total mean absolute deviation) for the very large and chemically diverse GMTKN55 benchmark to an unprecedented 1.17 kcal/mol, competitive with much costlier composite wave function ab initio approaches. Intriguingly, (a) the introduction of makes an empirical dispersion correction redundant; (b) generalized gradient approximation (GGA) or meta-GGA semilocal correlation functionals offer no advantage over the local density approximation (LDA) in this framework; (c) if a dispersion correction is retained, then simple Slater exchange leads to no significant loss in accuracy.

Exploring Avenues beyond Revised DSD Functionals: II. Random-Phase Approximation and Scaled MP3 Corrections.

For revDSD double hybrids, the Görling-Levy second-order perturbation theory component is an Achilles' heel when applied to systems with significant near-degeneracy ("static") correlation. We have explored its replacement by the direct random phase approximation (dRPA), inspired by the SCS-dRPA75 functional of Kállay and co-workers. The addition to the final energy of both a D4 empirical dispersion correction and of a semilocal correlation component lead to significant improvements, with DSD-PBEdRPA-D4 approaching the performance of revDSD-PBEP86-D4 and the Berkeley ωB97M(2).

Canonical and DLPNO-Based Composite Wavefunction Methods Parametrized against Large and Chemically Diverse Training Sets. 2: Correlation-Consistent Basis Sets, Core-Valence Correlation, and F12 Alternatives.

A hierarchy of wavefunction composite methods (cWFT), based on G4-type cWFT methods available for elements H through Rn, was recently reported by the present authors [ 2020, 16, 4238]. We extend this hierarchy by considering the inner-shell correlation energy in the second-order Møller-Plesset correction and replacing the Weigend-Ahlrichs def2-ZVPP(D) basis sets used with complete basis set extrapolation from augmented correlation-consistent core-valence triple-ζ, aug-cc-pwCVTZ(-PP), and quadruple-ζ, aug-cc-pwCVQZ(-PP), basis sets, thus creating cc-G4-type methods. For the large and chemically diverse GMTKN55 benchmark suite, they represent a substantial further improvement and bring WTMAD2 (weighted mean absolute deviation) down below 1 kcal/mol.

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?

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.

Argo: a data analysis program for quantum chemical calculations.

The ARGO program is designed for the analysis and display of results obtained from quantum chemical calculations. ARGO currently extracts values of geometrical parameters and energy of each conformer obtained from potential energy surface (PES) scans. It automatically arranges the data into columns and prepares input files for the Gnuplot graphing utility for two- and three-dimensional PES graphs.