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 C4 clusters, presented here, illustrate the capabilities of the proposed methodology.
Original language | English (US) |
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Pages (from-to) | 6685-6693 |
Number of pages | 9 |
Journal | The Journal of chemical physics |
Volume | 93 |
Issue number | 9 |
DOIs | |
State | Published - 1990 |
ASJC Scopus subject areas
- General Physics and Astronomy
- Physical and Theoretical Chemistry