Remarkable Accuracy of an O(N6) Perturbative Correction to Opposite-Spin
CCSD: Are Triples Necessary for Chemical Accuracy in Coupled Cluster?
Posted on 2020-06-26 - 20:43
The
focus of this work is OS-CCSD-SPT(2), which is a second-order
similarity transformed perturbation theory correction to opposite
spin coupled cluster singles doubles, where in the latter the same-spin
amplitudes are removed and the opposite-spin ones are solved self-consistently.
OS-CCSD-SPT(2) is free of empirical parameters, has an instrinsic
scaling of O(N6), and
makes no use of triples. We demonstrate that, for non-multireference
molecules, OS-CCSD-SPT(2) produces relative energies whose accuracy
is significantly higher than what is generally expected of a triples-free
model. For example, using PBE0 orbitals in the reference, OS-CCSD-SPT(2)
exhibits a mean absolute deviation (MAD) of 1.13 kcal/mol with respect
to CCSD(2F) benchmark values for the non-multireference
subset of W4-08 atomization energies (cf. a MAD > 6.5 kcal/mol
for
CCSD) and a MAD of 0.68 kcal/mol for the energies of reactions generated
from the W4-08 molecules. These MADs are reduced to 0.61 and 0.63
kcal/mol, respectively, by a simple one-parameter spin-component scaling
of the OS-CCSD-SPT(2) same-spin correlation energy. OS-CCSD is also
naturally amenable to higher order corrections: the associated third-order
correction, OS-CCSD-SPT(3), which does involve connected triples and
quadruples, exhibits a MAD of 0.44 kcal/mol for the same atomization-energy
benchmark.
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Small, David W. (2020). Remarkable Accuracy of an O(N6) Perturbative Correction to Opposite-Spin
CCSD: Are Triples Necessary for Chemical Accuracy in Coupled Cluster?. ACS Publications. Collection. https://doi.org/10.1021/acs.jctc.0c00244
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AUTHORS (1)
DS
David W. Small
KEYWORDS
PBE 0 orbitalsnon-multireference subsetN 6MADRemarkable Accuracyone-parameter spin-componentperturbation theory correctionW 4-08 atomization energiesorder correctionsopposite-spin onesatomization-energy benchmarkbenchmark valueskcalW 4-08 moleculessame-spin amplitudesChemical Accuracytriples-free modelnon-multireference moleculesPerturbative Correctionthird-order correctionOpposite-Spin CCSDOS-CCSDOS-CCSD-SPTcluster singles doubles