W4$\Lambda$: leveraging $\Lambda$ coupled cluster for accurate computational thermochemistry approaches

Abstract

High-accuracy composite wavefunction methods like Weizmann-4 (W4) theory, high-accuracy extrapolated \textit{ab initio} thermochemistry (HEAT), and Feller-Peterson-Dixon (FPD) 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 lambda coupled cluster expansion converges more rapidly and smoothly than the regular coupled cluster series. By means of CCSDT(Q)${}_{\Lambda }$ and CCSDTQ(5)${}_{\Lambda }$, we can considerably (up to an order of magnitude) accelerate W4- and W4.3-type calculations without loss in accuracy, leading to the W4$\Lambda$ and W4.3$\Lambda$ computational thermochemistry protocols.

arXiv commentJ. Phys. Chem. A 128, 1715-1724 (2024). PDF is CC:BY 4.0

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• Factorized Quadruples and a Predictor of Higher-Level Correlation in Thermochemistry
• FNO-CCSDTQ(5)${}_{\Lambda }$ as an economical alternative for connected quintuple excitations contributions in coupled cluster thermochemistry
• A new open-shell CCSDTQ implementation and its application to the basis set convergence of post-CCSDT(Q) corrections in computational thermochemistry