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Multi-state Multireference Rayleigh–Schrödinger Perturbation Theory for Mixed Electronic States: Second and Third Order

Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
Int. J. Mol. Sci. 2002, 3(6), 639-655; https://0-doi-org.brum.beds.ac.uk/10.3390/i3060639
Received: 12 December 2001 / Accepted: 20 March 2002 / Published: 30 June 2002
(This article belongs to the Special Issue Multireference Quantum Chemical Methods)
The formalism for multi-state multireference configuration-based Rayleigh-Schrödinger perturbation theory and procedures for its implementation for the second-order and third-order energy within a multireference configuration interaction computer program are reviewed. This formalism is designed for calculations on electronic states that involve strong mixing between different zero-order contributions, such as avoided crossings or mixed valence-Rydberg states. Such mixed states typically display very large differences in reference-configuration mixing coefficients between the reference MCSCF wave function and an accurate correlated wave function, differences that cannot be reflected in state-specific (diagonalize-then-perturb) multireference perturbation theory through third order. A procedure described in detail applies quasidegenerate perturbation theory based on a model space of a few state-averaged MCSCF functions for the states expected to participate strongly in the mixing, and can be characterized as a “diagonalize-then-perturb-thendiagonalize” approach. It is similar in various respects to several published methods, including an implementation by Finley, Malmqvist, Roos, and Serrano-Andrés [Chem. Phys. Lett. 1998, 288, 299–306]. View Full-Text
Keywords: Perturbation theory; multireference; mixed states; avoided crossings; ab initio Perturbation theory; multireference; mixed states; avoided crossings; ab initio
MDPI and ACS Style

Shavitt, I. Multi-state Multireference Rayleigh–Schrödinger Perturbation Theory for Mixed Electronic States: Second and Third Order. Int. J. Mol. Sci. 2002, 3, 639-655. https://0-doi-org.brum.beds.ac.uk/10.3390/i3060639

AMA Style

Shavitt I. Multi-state Multireference Rayleigh–Schrödinger Perturbation Theory for Mixed Electronic States: Second and Third Order. International Journal of Molecular Sciences. 2002; 3(6):639-655. https://0-doi-org.brum.beds.ac.uk/10.3390/i3060639

Chicago/Turabian Style

Shavitt, Isaiah. 2002. "Multi-state Multireference Rayleigh–Schrödinger Perturbation Theory for Mixed Electronic States: Second and Third Order" International Journal of Molecular Sciences 3, no. 6: 639-655. https://0-doi-org.brum.beds.ac.uk/10.3390/i3060639

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