Here, the Coupled Cluster Valence Bond (CCVB) method, previously presented for closed-shell (CS) systems, is extended to open-shell (OS) systems. The theoretical development is based on embedding the basic OS CCVB wavefunction in a fictitious singlet super-system. This approach reveals that the OS CCVB amplitude equations are quite similar to those of CS CCVB, and thus that OS CCVB requires the same level of computational effort as CS CCVB, which is an inexpensive method. We present qualitatively correct CCVB potential energy curves for all low-lying spin states of P2 and Mn2+. CCVB is successfully applied to the low-lying spin states of some model linear polycarbenes, systems that appear to be a hindrance to standard density functionals. We examine an octa-carbene dimer in a side-by-side orientation, which, in the monomer dissociation limit, exhibits maximal strong correlation over the length of the polycarbene.
Small, David W. and Head-Gordon, Martin. "Coupled cluster valence bond theory for open-shell systems with application to very long range strong correlation in a polycarbene dimer." Journal of Chemical Physics, vol. 147, no. 2, Jul. 2017. https://doi.org/10.1063/1.4991797
Small, David W., & Head-Gordon, Martin (2017). Coupled cluster valence bond theory for open-shell systems with application to very long range strong correlation in a polycarbene dimer. Journal of Chemical Physics, 147(2). https://doi.org/10.1063/1.4991797
Small, David W., and Head-Gordon, Martin, "Coupled cluster valence bond theory for open-shell systems with application to very long range strong correlation in a polycarbene dimer," Journal of Chemical Physics 147, no. 2 (2017), https://doi.org/10.1063/1.4991797
@article{osti_1477258,
author = {Small, David W. and Head-Gordon, Martin},
title = {Coupled cluster valence bond theory for open-shell systems with application to very long range strong correlation in a polycarbene dimer},
annote = {Here, the Coupled Cluster Valence Bond (CCVB) method, previously presented for closed-shell (CS) systems, is extended to open-shell (OS) systems. The theoretical development is based on embedding the basic OS CCVB wavefunction in a fictitious singlet super-system. This approach reveals that the OS CCVB amplitude equations are quite similar to those of CS CCVB, and thus that OS CCVB requires the same level of computational effort as CS CCVB, which is an inexpensive method. We present qualitatively correct CCVB potential energy curves for all low-lying spin states of P2 and Mn2+. CCVB is successfully applied to the low-lying spin states of some model linear polycarbenes, systems that appear to be a hindrance to standard density functionals. We examine an octa-carbene dimer in a side-by-side orientation, which, in the monomer dissociation limit, exhibits maximal strong correlation over the length of the polycarbene.},
doi = {10.1063/1.4991797},
url = {https://www.osti.gov/biblio/1477258},
journal = {Journal of Chemical Physics},
issn = {ISSN 0021-9606},
number = {2},
volume = {147},
place = {United States},
publisher = {American Institute of Physics (AIP)},
year = {2017},
month = {07}}
Hurley, A. C.; Lennard-Jones, John Edward; Pople, John Anthony
Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, Vol. 220, Issue 1143, p. 446-455https://doi.org/10.1098/rspa.1953.0198