Journal ArticleDOI
Cluster expansion of the wavefunction. Symmetry-adapted-cluster expansion, its variational determination, and extension of open-shell orbital theory
H. Nakatsuji,Kimihiko Hirao +1 more
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In this paper, the symmetry-adapted cluster expansion of an exact wave function has been studied, which is suitable for open-shell systems as well as closed-shell ones.Abstract:
The symmetry‐adapted‐cluster (SAC) expansion of an exact wavefunction is given. It is constructed from the generators of the symmetry‐adapted excited configurations having the symmetry under consideration, and includes their higher‐order effect and self‐consistency effect. It is different from the conventional cluster expansions in several important points, and is suitable for applications to open‐shell systems as well as closed‐shell systems. The variational equation for the SAC wavefunction has a form similar to the generalized Brillouin theorem in accordance with the inclusion of the higher‐order effect and the self‐consistency effect. We have expressed some existing open‐shell orbital theories equivalently in the conventional cluster expansion formulas, and on this basis, we have given the pseudo‐orbital theory which is an extension of open‐shell orbital theory in the SAC expansion formula.read more
Citations
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Single-reference ab initio methods for the calculation of excited states of large molecules.
Andreas Dreuw,Martin Head-Gordon +1 more
Journal ArticleDOI
Coupled cluster theory for high spin, open shell reference wave functions
TL;DR: In this paper, the coupled cluster method restricted to single and double excitations (CCSD) is considered for the case of a spin restricted Hartree-Fock open shell reference determinant.
Journal ArticleDOI
Equation-of-Motion Coupled-Cluster Methods for Open-Shell and Electronically Excited Species: The Hitchhiker's Guide to Fock Space
TL;DR: This review provides a guide to established EOM methods illustrated by examples that demonstrate the types of target states currently accessible by EOM, and touches on some formal aspects of the theory and important current developments.
Journal ArticleDOI
Multireference Møller-Plesset method
TL;DR: In this paper, a multireference Moller-Plesset method is derived for 2-configuration MCSCF wavefunctions in which only two electrons are correlated, and potential curves for H 2, HF and F 2 molecules agree well with the full or near-full CI results.
Journal ArticleDOI
The equation-of-motion coupled-cluster method: Excitation energies of Be and CO
TL;DR: In this paper, an equation of motion coupled-cluster (EOM-CC) method for the calculation of excitation energies is presented, which is based upon representing an excited state as an excitation from a ground state and the excitation energy is obtained by solving a non-Hermitian eigenvalue problem.
References
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Journal ArticleDOI
On the Correlation Problem in Atomic and Molecular Systems. Calculation of Wavefunction Components in Ursell-Type Expansion Using Quantum-Field Theoretical Methods
TL;DR: In this article, a method for the calculation of the matrix elements of the logarithm of an operator which gives the exact wavefunction when operating on the wavefunction in the one-electron approximation is proposed.
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Self-Consistent Field Theory for Open Shells of Electronic Systems
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Correlation Problems in Atomic and Molecular Systems. IV. Extended Coupled-Pair Many-Electron Theory and Its Application to the B H 3 Molecule
Josef Paldus,J. Čížek,I. Shavitt +2 more
TL;DR: In this article, the equations of coupled-pair many-electron theory (CPMET) were extended to incorporate the effect of both unlinked and linked triexcited clusters, and the minimal basis correlation energy of the B${\mathrm{H}}_{3}$ molecule in the ground state was calculated using the ordinary as well as extended CPMET in various degrees of approximation.
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Stability conditions and nuclear rotations in the Hartree-Fock theory
TL;DR: In this article, the moment of inertia of an axially symmetric system is derived within the framework of the Hartree-Fock theory, and the expression for a determinant is generalized to include the type of wave functions used in the theory of superconductivity.
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Stability Conditions for the Solutions of the Hartree—Fock Equations for Atomic and Molecular Systems. Application to the Pi‐Electron Model of Cyclic Polyenes
J. Čížek,Josef Paldus +1 more
TL;DR: In this paper, the Hartree-Fock determinant minimization of the energy expectation value was derived using the language familiar in quantum chemistry and the stability conditions for closed-shell electronic systems were specified.