Term: complete active space self-consistent field second-order perturbation theory (CASPT2)
https://doi.org/10.1351/goldbook.CT07344

Definition:
Theoretical scheme suitable for computations of accurate excitation energies and reaction barriers. In the first step, electron correlation is taken into account only to a certain extent by using a CASSCF formalism (the so called non-dynamic correlation), whereas the remaining electron correlation (the so called dynamic correlation) is included through the use of second-order perturbation theory.

Related Terms:
1) electron correlation (http://doi.org/10.1351/goldbook.E01984).
2) perturbation theory (http://doi.org/10.1351/goldbook.PT07090).

Source: PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 316 (https://doi.org/10.1351/pac200779030293)

Citation: 'complete active space self-consistent field second-order perturbation theory (CASPT2)' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.CT07344

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