New perspectives in multireference perturbation theory: the n-electron valence state approach |
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Authors: | Celestino Angeli Mariachiara Pastore Renzo Cimiraglia |
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Institution: | (1) Dipartimento di Chimica, Università di Ferrara, Via Borsari 46, 44100 Ferrara, Italy |
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Abstract: | The n-electron valence state perturbation theory (NEVPT) is a form of multireference perturbation theory which is based on a zero
order reference wavefunction of CAS-CI type (complete active space configuration interaction) and which is characterized by
the utilization of correction functions (zero order wavefunctions external to the CAS) of multireference nature, obtained
through the diagonalization of a suitable two-electron model Hamiltonian (Dyall’s Hamiltonian) in some well defined determinant
spaces. A review of the NEVPT approach is presented, starting from the original second order state-specific formulation, going
through the quasidegenerate multi-state extension and arriving at the recent implementations of the third order in the energy
and of the internally contracted configuration interaction. The chief properties of NEVPT—size consistence and absence of
intruder states—are analyzed. Finally, an application concerning the calculation of the vertical spectrum of the biologically
important free base porphin molecule, is presented. |
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Keywords: | Multireference perturbation theory NEVPT Internally contracted CI Free base porphin |
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