Toward a W4-F12 approach: Can explicitly correlated and orbital-based ab initio CCSD(T) limits be reconciled?

Abstract

In the context of high-accuracy computational thermochemistry, the valence CCSD correlation component of molecular atomization energies present the most severe basis set convergence problem, followed by the (T) component. In the present paper, we make a detailed comparison, for an expanded version of the W4-11 thermochemistry benchmark, between on the one hand 2 orbital-based CCSD/AV{5,6}Z+d and CCSD/ACV{5,6}Z extrapolation, and on the other hand CCSD-F12b calculations with cc-pVQZ-F12 and cc-pV5Z-F12 basis sets. This latter basis set, now available for H-He, B-Ne, and Al-Ar, is shown to be very close to the basis set limit. 3

Energetic and spectroscopic properties of the low-lying C7H2 isomers: a high-level ab initio perspective

“…80 In order to obtain reliable relative energies for isomers 1-9, high-level benchmark data have been obtained using the W3lite-F12 theory. 64,66 The W3lite-F12 theory (and its earlier version, the W3.2lite theory) [81][82][83] represents layered extrapolations to the relativistic, all-electron CCSDT(Q)/CBS limit and can achieve near-benchmark accuracy for atomization reactions (i.e., they are associated with root-mean-square deviations, RMSDs, from accurate atomization energies of about 1 kJ mol À1 = 0.24 kcal mol…”

“…64 For example, the related W3-F12 theory is associated with an RMSD of 0.27 kcal mol À1 for a set of 140 very accurate atomization energies obtained at the full configuration interaction (FCI) infinite basis-set limit. 64,66,81,83 The…”

W4‐17: A diverse and high‐confidence dataset of atomization energies for benchmarking high‐level electronic structure methods

“…[1][2][3][4] The same trend is expected along a generalization of this hierarchy, namely, the connectivity-based hierarchical (CBHn) reaction scheme, in the sequence: atomization (CBH-0) ! [1,[21][22][23] Atomization reactions are therefore of special interest in the evaluation and development of approximate quantum chemical methods as they serve as the ultimate test for these procedures. bond-centric (CBH-2), and so forth.…”

“…branched alkane isomerizations is significantly better than that for isogyric structural isomerizations. [21][22][23] The TAEs for 33 larger systems (e.g., C 2 F 6 , C 2 Cl 6 , SF 6 , and C 6 H 6 ) were obtained at the CCSDT(Q)/ CBS level of theory by means of the W4lite thermochemical protocol. branched alkane isomerizations (i.e., reactions that conserve the number of C atoms in each hybridization state in addition to being isodesmic) vary between $0.1-1 kcal mol 21 .…”

“…[10][11][12][13][14][15][16][17][18][19][20] For example, the root mean square deviations (RMSDs) for a wide range of dispersion-corrected DFT methods for linear ! [21,22] In the present work, we will use the W4-17 database to evaluate the performance of a wide range of composite methods that attempt to approximate the coupled-cluster energy with singles, doubles, and quasiperturbative triple excitations (CCSD(T)) at various degrees of basis-set completeness. [5] The RMSDs for isodesmic reactions involving alkanes vary between $0.3-3 kcal mol 21 , while for alkane atomization reactions they vary between $2-25 kcal mol 21 .…”