Issue 12, 2003

Approaching closed-shell accuracy for radicals using coupled cluster theory with perturbative triple substitutions

Abstract

The erratic performance of CCSD(T) for radicals is analyzed using non-Hartree–Fock references as a starting point for correlations and by testing the (2) approach as an alternative to (T) for including higher-order correlation effects. Though CCSD(2) improves upon CCSD(T), correlating from a better-behaved reference makes both theories robust. Comparisons of calculated harmonic frequencies against experiment in a set of diatomic radicals from Brueckner-like orbitals demonstrate improvement approaching closed-shell accuracy. Additionally, we find that using BLYP Kohn–Sham orbitals yields similar improvements, and they are therefore a useful, inexpensive reference for high-level correlation methods in difficult systems. Root-mean-square errors of 1.0–1.2% are found in the cc-pVQZ basis for predicted harmonic frequencies in the test set using OD(T) and KS-CCSD(T), making these approaches quite competitive with CCSD(T) for closed-shell molecules. Finally, these improvements are correlated with spin contamination and the rate of change of the electron density with nuclear displacement.

Article information

Article type
Paper
Submitted
21 Feb 2003
Accepted
24 Apr 2003
First published
09 May 2003

Phys. Chem. Chem. Phys., 2003,5, 2488-2493

Approaching closed-shell accuracy for radicals using coupled cluster theory with perturbative triple substitutions

G. J. O. Beran, S. R. Gwaltney and M. Head-Gordon, Phys. Chem. Chem. Phys., 2003, 5, 2488 DOI: 10.1039/B304542K

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements