### Abstract

The second-order Hylleraas functional and the Newton-Raphson optimization technique have been used to generate first-order correlation orbitals (FOCOs) for the spin-unrestricted Hartree-Fock (UHF) zero-order wave function. The correlation orbitals are linear combinations of the UHF virtual orbitals and are different for electrons with α and β spins. We show that even the number of FOCOs is significantly reduced with respect to the number of all UHF virtual orbitals, the decrease of the second-order correlation energy is rather small. The primary application of the FOCO UHF method is to study larger open-shell molecular systems at higher correlated levels of the theory. The coupled-cluster calculations with FOCOs on the electron affinities of the linear and rhombic carbon C_{4} clusters, presented here, illustrate the capabilities of the proposed methodology.

Original language | English (US) |
---|---|

Pages (from-to) | 6685-6693 |

Number of pages | 9 |

Journal | The Journal of Chemical Physics |

Volume | 93 |

Issue number | 9 |

State | Published - 1990 |

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### ASJC Scopus subject areas

- Atomic and Molecular Physics, and Optics

### Cite this

**First-order correlation orbitals for the spin-unrestricted Hartree-Fock zero-order wave function. Electron affinities of C _{4} clusters.** / Adamowicz, Ludwik.

Research output: Contribution to journal › Article

}

TY - JOUR

T1 - First-order correlation orbitals for the spin-unrestricted Hartree-Fock zero-order wave function. Electron affinities of C4 clusters

AU - Adamowicz, Ludwik

PY - 1990

Y1 - 1990

N2 - The second-order Hylleraas functional and the Newton-Raphson optimization technique have been used to generate first-order correlation orbitals (FOCOs) for the spin-unrestricted Hartree-Fock (UHF) zero-order wave function. The correlation orbitals are linear combinations of the UHF virtual orbitals and are different for electrons with α and β spins. We show that even the number of FOCOs is significantly reduced with respect to the number of all UHF virtual orbitals, the decrease of the second-order correlation energy is rather small. The primary application of the FOCO UHF method is to study larger open-shell molecular systems at higher correlated levels of the theory. The coupled-cluster calculations with FOCOs on the electron affinities of the linear and rhombic carbon C4 clusters, presented here, illustrate the capabilities of the proposed methodology.

AB - The second-order Hylleraas functional and the Newton-Raphson optimization technique have been used to generate first-order correlation orbitals (FOCOs) for the spin-unrestricted Hartree-Fock (UHF) zero-order wave function. The correlation orbitals are linear combinations of the UHF virtual orbitals and are different for electrons with α and β spins. We show that even the number of FOCOs is significantly reduced with respect to the number of all UHF virtual orbitals, the decrease of the second-order correlation energy is rather small. The primary application of the FOCO UHF method is to study larger open-shell molecular systems at higher correlated levels of the theory. The coupled-cluster calculations with FOCOs on the electron affinities of the linear and rhombic carbon C4 clusters, presented here, illustrate the capabilities of the proposed methodology.

UR - http://www.scopus.com/inward/record.url?scp=0011742761&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0011742761&partnerID=8YFLogxK

M3 - Article

VL - 93

SP - 6685

EP - 6693

JO - Journal of Chemical Physics

JF - Journal of Chemical Physics

SN - 0021-9606

IS - 9

ER -