Post-CCSD(T) corrections to bond distances and vibrational frequencies: the power of $\Lambda$

Abstract

The importance of post-CCSD(T) corrections as high as CCSDTQ56 for ground-state spectroscopic constants ($D_e$, ${\omega }_e$, ${\omega }_e{x}_e$, and ${\alpha }_e$) has been surveyed for a sample of two dozen mostly heavy-atom diatomics spanning a broad range of static correlation strength. While CCSD(T) is known to be an unusually felicitous `Pauling point' between accuracy and computational cost, performance leaves something to be desired for molecules with strong static correlation. We find CCSDT(Q)${}_{\Lambda }$ to be the next `sweet spot' up, of comparable or superior quality to the much more expensive CCSDTQ. A similar comparison applies to CCSDTQ(5)${}_{\Lambda }$ vs. CCSDTQ5, while CCSDTQ5(6)${}_{\Lambda }$ is essentially indistinguishable from CCSDTQ56. A composite of CCSD(T)-X2C/ACV5Z-X2C with [CCSDT(Q)${}_{\Lambda }$ -- CCSD(T)]/cc-pVTZ or even cc-pVDZ basis sets appears highly effective for computational vibrational spectroscopy. Unlike CCSDT(Q) which breaks down for the ozone vibrational frequencies, CCSDT(Q)${}_{\Lambda }$ handles them gracefully.

Mol. Phys., in press [Timothy J. Lee memorial issue]

References in corpus (2)

• W4 theory for computational thermochemistry: in pursuit of confident sub-kJ/mol predictions
• Basis set convergence of post-CCSD contributions to molecular atomization energies

Cited by in corpus (5)

• W4$\Lambda$: leveraging $\Lambda$ coupled cluster for accurate computational thermochemistry approaches
• Can G4-like Composite Ab Initio Methods Accurately Predict Vibrational Harmonic Frequencies?
• Factorized Quadruples and a Predictor of Higher-Level Correlation in Thermochemistry
• On the performance of HRPA(D) for NMR spin-spin coupling constants: Smaller molecules, aromatic and fluoroaromatic compounds
• Modelling Triatomic Biosignatures: Ozone and Isotopomers