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Abstract
© 2016 Author(s).In the context of highaccuracy computational thermochemistry, the valence coupled cluster with all singles and doubles (CCSD) correlation component of molecular atomization energies presents 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 W411 thermochemistry benchmark, between, on the one hand, orbitalbased CCSD/AV{5,6}Z + d and CCSD/ACV{5,6}Z extrapolation, and on the other hand CCSDF12b calculations with ccpVQZF12 and ccpV5ZF12 basis sets. This latter basis set, now available for HHe, BNe, and AlAr, is shown to be very close to the basis set limit. Apparent differences (which can reach 0.35 kcal/mol for systems like CCl4) between orbitalbased and CCSDF12b basis set limits disappear if basis sets with additional radial flexibility, such as ACV{5,6}Z, are used for the orbital calculation. Counterpoise calculations reveal that, while total atomization energies with V5ZF12 basis sets are nearly free of BSSE, orbital calculations have significant BSSE even with AV(6 + d)Z basis sets, leading to nonnegligible differences between raw and counterpoisecorrected extrapolated limits. This latter problem is greatly reduced by switching to ACV{5,6}Z corevalence basis sets, or simply adding an additional zeta to just the valence orbitals. Previous reports that allelectron approaches like HEAT (highaccuracy extrapolated abinitio thermochemistry) lead to different CCSD(T) limits than "valence limit + CV correction" approaches like FellerPetersonDixon and Weizmann4 (W4) theory can be rationalized in terms of the greater radial flexibility of corevalence basis sets. For (T) corrections, conventional CCSD(T)/AV{Q,5}Z + d calculations are found to be superior to scaled or extrapolated CCSD(T)F12b calculations of similar cost. For a W4F12 protocol, we recommend obtaining the HartreeFock and valence CCSD components from CCSDF12b/ccpV{Q,5}ZF12 calculations, but the (T) component from conventional CCSD(T)/aug’ccpV{Q,5}Z + d calculations using Schwenke’s extrapolation; postCCSD(T), corevalence, and relativistic corrections are to be obtained as in the original W4 theory. W4F12 is found to agree slightly better than W4 with ATcT (active thermochemical tables) data, at a substantial saving in computation time and especially I/O overhead. A W4F12 calculation on benzene is presented as a proof of concept.
Original language  English 

Article number  214101 
Pages (fromto)  214101121410113 
Journal  Journal of Chemical Physics 
Volume  144 
Issue number  21 
Early online date  1 Jun 2016 
DOIs  
Publication status  Published  7 Jun 2016 
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 1 Finished

Mimicking nature: computational design of better antioxidants
ARC Australian Research Council
1/01/14 → 31/05/17
Project: Research