Lewis structures and Feynman diagrams: The treatment of geminal correlation in Fock space

Scaled Feynman diagrams are proposed as perturbative corrections to the total energy. The proposal is tested by calculating potential energy curves for the valence states of the cyano radical. Unique features of the valence state are part of the starting approximation. The latter is computed with a standard quantum chemical method. For a particular method, the scale is independent of the valence state. At each bond distance, one set of quasiparticles and Feynman diagrams is used for all valence states. Scaling will be useful whenever perturbative corrections can be expressed with Feynman diagrams. In the cyano radical, competition for the odd electron between the σ and π orbitals produces a variety of valence states. Many are quasidegenerate. The 16 states investigated here are doublets and quartets with triple bonds, double bonds, 'resonance' bonds, bonds intermediate to double and triple bonds, and bonds intermediate to single and double bonds. Energy curves and spectroscopic constants are reported for the lowest lying quartets and two or more lowest doublets of ± , , and symmetries, and also 1 2 symmetry. Inner and outer minima in the energy curve for 3 2 are assigned to H and G, respectively. A more accurate assignment of a 4 + is made. Relative to experiment, maximum (average) errors in bond distance, frequency, and the adiabatic excitation energy are 1.6 pm (1 pm), 60 cm −1 (50 cm −1 ), and 19 kJ/mol (5 kJ/mol), respectively. The error in the ground state dissociation energy is 11 kJ/mol. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 90: 516-533, 2002

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Optimization of density matrix functionals by the Hartree–Fock–Bogoliubov method

Staroverov

Scuseria

2002

The Journal of Chemical Physics

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It is demonstrated that the “corrected Hartree–Fock” (CHF) density matrix functional proposed by Csányi and Arias is identical with the Hartree–Fock–Bogoliubov (HFB) functional of the generalized density matrix up to the sign of the pairing energy term. Using this analogy, variational CHF calculations can be performed much more efficiently by solving the HFB equations for the generalized density matrix than by optimizing separately the natural orbitals and their occupations numbers. A family of CHF-type functionals with a scaled pairing energy is introduced and compared to the closely related antisymmetrized geminal power method.

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Lewis structures and Feynman diagrams: The treatment of geminal correlation in Fock space

Cited by 4 publications

References 49 publications

The Algebra of Effective Hamiltonians and Operators: Exact Operators

The Algebra of Effective Hamiltonians and Operators: Exact Operators

Valence states of the cyano radical Feynman's way

Optimization of density matrix functionals by the Hartree–Fock–Bogoliubov method

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