FNO-CCSDTQ(5)Λ as an economical alternative for connected quintuple excitations contributions in coupled cluster thermochemistry
Abstract
Contributions from connected quintuple excitations in coupled cluster theory can reach the 0.5 kcal mol − 1 range, important enough to matter in accurate computational thermochemistry, yet the very steep ∝ N 12 CPU time scaling impedes routine evaluation. We show that for the differential contribution of quintuples, convergence of a frozen natural orbital (FNO) expansion with respect to the NO cutoff is rapid enough to make FNO-CCSDTQ(5) Λ with cutoffs of 0.0025 or 0.001 viable alternatives. A naive extrapolation to zero cutoff from {0.005,0.0025} works surprisingly well as a low-cost option. Interestingly, FNO convergence is definitely slower for second-row than for first-row compounds.
Fields of Study & Subjects
Advanced Chemical Physics Studies
Phase Equilibria and Thermodynamics
Chemical Thermodynamics and Molecular Structure
Publication details
- Journal / source
- Chemical Physics Letters
- Publisher
- Elsevier BV
- Volume
- 897
- Pages
- 142951–142951
- Publication date
- 14 July 2026
- Language
- EN