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Multiconfigurational perturbation theory
Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science. Karlstad University, Faculty of Economic Sciences, Communication and IT, Centre for HumanIT.ORCID iD: 0000-0001-6302-7006
1992 (English)Doctoral thesis, monograph (Other academic)
Abstract [en]

The aim of the thesis is to analyze a method which describes the electron correlation in atoms and molecules. The method is based on Rayleigh-Schrödinger perturbation theory with a partitioning of the Hamiltonian into a fairly simple zeroth-order operator and a perturbation operator. The zeroth-order Hamiltonian is founded on a one-electron Fock-type operator and two different operators have been tested. The zeroth-order wave function is constructed from a complete active space self-consistent field (CASSCF) calculation. This means that the zeroth-order wave function for open-shell systems and systems with strong configurational mixing (near degeneracy) can be obtained on an equal level as closed-shell (single determinant) states. The theory is formulated in such a way that the Möller-Plesset perturbation theory is obtained for the closed-shell (single determinant) state. The flexibility of the CASSCF method makes it possible, in principle, to construct the zeroth-order wave function (and the zeroth-order Hamiltonian) to any desired accuracy. The perturbation expansion of the energy is therefore expected to converge fast and only up to the second-order contribution has been implemented leading to fairly fast and accurate calculations. The aim of the computer implementation is to describe the electron correlation in small and medium-sized molecules (up to 20 atoms) accurately. The application of the perturbation method to a number of problems in chemistry is demonstrated in the thesis: (1) the calculation of electronic properties and harmonic vibrational frequencies of the ozone molecule; (2) the calculation of electric dipole polarizabilities of excited valence states of several first- and second-row atoms; (3) the calculation of excited states of the nickel atom, the benzene molecule, and the azabenzenes pyridine, pyrazine, pyridazine, and s-triazine

Place, publisher, year, edition, pages
Lund, 1992.
Keyword [en]
Electron correlation, CASSCF, multiconfigurational second-order perturbation theory, CASPT2, ozone, C, N, O, F, Si, P, S, Cl, Ni, benzene, pyridine, pyrazine, pyrimidine, pyridazine, s-triazine, electric properties, excited states, spectroscopic data
Identifiers
URN: urn:nbn:se:kau:diva-21628ISBN: 9162806149OAI: oai:DiVA.org:kau-21628DiVA: diva2:595302
Available from: 2013-01-21 Created: 2013-01-21 Last updated: 2014-10-13

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