Strongly correlated mechanisms of a photoexcited radical reaction from the anti-Hermitian contracted Schroedinger equation
- Department of Chemistry and James Franck Institute, University of Chicago, Chicago, Illinois 60637 (United States)
Photoexcited radical reactions are critical to processes in both nature and materials, and yet they can be challenging for electronic structure methods due to the presence of strong electron correlation. Reduced-density-matrix (RDM) methods, based on solving the anti-Hermitian contracted Schroedinger equation (ACSE) for the two-electron RDM (2-RDM), are examined for studying the strongly correlated mechanisms of these reactions with application to the electrocyclic interconversion of allyl and cyclopropyl radicals. We combine recent extensions of the ACSE to excited states [G. Gidofalvi and D. A. Mazziotti, Phys. Rev. A 80, 022507 (2009)] and arbitrary spin states [A. E. Rothman, J. J. Foley IV, and D. A. Mazziotti, Phys. Rev. A 80, 052508 (2009)]. The ACSE predicts that the ground-state ring closure of the allyl radical has a high 52.5 kcal/mol activation energy that is consistent with experimental data, while the closure of an excited allyl radical can occur by disrotatory and conrotatory pathways whose transition states are essentially barrierless. Comparisons are made with multireference second- and third-order perturbation theories and multireference configuration interaction. While predicted energy differences do not vary greatly between methods, the ACSE appears to improve these differences when they involve a strongly and a weakly correlated radical by capturing a greater share of single-reference correlation that increases the stability of the weakly correlated radicals. For example, the ACSE predicts a -39.6 kcal/mol conversion of the excited allyl radical to the ground-state cyclopropyl radical in comparison to the -32.6 to -37.3 kcal/mol conversions predicted by multireference methods. In addition, the ACSE reduces the computational scaling with the number of strongly correlated orbitals from exponential (traditional multireference methods) to quadratic. Computed ground- and excited-state 2-RDMs are nearly N-representable.
- OSTI ID:
- 21559979
- Journal Information:
- Journal of Chemical Physics, Vol. 134, Issue 3; Other Information: DOI: 10.1063/1.3526298; (c) 2011 American Institute of Physics; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ACTIVATION ENERGY
ALLYL RADICALS
COMPARATIVE EVALUATIONS
CONFIGURATION INTERACTION
DENSITY MATRIX
ELECTRON CORRELATION
ELECTRONIC STRUCTURE
ELECTRONS
EXCITED STATES
GROUND STATES
ORGANIC COMPOUNDS
PERTURBATION THEORY
PHOTOCHEMISTRY
PHOTON-MOLECULE COLLISIONS
REACTION KINETICS
SCHROEDINGER EQUATION
STABILITY
ALKYL RADICALS
CHEMISTRY
COLLISIONS
CORRELATIONS
DIFFERENTIAL EQUATIONS
ELEMENTARY PARTICLES
ENERGY
ENERGY LEVELS
EQUATIONS
EVALUATION
FERMIONS
KINETICS
LEPTONS
MATRICES
MOLECULE COLLISIONS
PARTIAL DIFFERENTIAL EQUATIONS
PHOTON COLLISIONS
RADICALS
WAVE EQUATIONS