Title: Multiconfigurational Second-Order Perturbation Theory Restricted Active Space (RASPT2) Studies on Mononuclear First-Row Transition-Metal Systems
Authors: Vancoillie, Steven
Zhao, Hailiang
Van Tan, Tran
Hendrickx, Marc
Pierloot, Kristine # ×
Issue Date: Dec-2011
Publisher: American Chemical Society
Series Title: Journal of Chemical Theory and Computation vol:7 pages:3961-3977
Abstract: A series of model transition-metal complexes, CrF6, ferrocene, Cr(CO)6, ferrous porphin, cobalt corrole, and
FeO/FeO(-), have been studied using second-order perturbation theory based on a restricted active space self-consistent field
reference wave function (RASPT2). Several important properties (structures, relative energies of different structural minima,
binding energies, spin state energetics, and electronic excitation energies) were investigated. A systematic investigation was
performed on the effect of: (a) the size and composition of the global RAS space, (b) different (RAS1/RAS2/RAS3) subpartitions of
the global RAS space, and (c) different excitation levels (out of RAS1/into RAS3) within the RAS space. Calculations with active
spaces, including up to 35 orbitals, are presented. The results obtained with smaller active spaces (up to 16 orbitals) were compared
to previous and current results obtained with a complete active space self-consistent field reference wave function (CASPT2). Highly
accurate RASPT2 results were obtained for the heterolytic binding energy of ferrocene and for the electronic spectrum of Cr(CO)6,
with errors within chemical accuracy. For ferrous porphyrin the intermediate spin 3A2g ground state is (for the first time with a wave
function-based method) correctly predicted, while its high magnetic moment (4.4 μB) is attributed to spin-orbit coupling with very
close-lying 5A1g and 3Eg states. The toughest case met in this work is cobalt corrole, for which we studied the relative energy of several
low-lying Co(II)-corrole π radical states with respect to the Co(III) ground state. Very large RAS spaces (25-33 orbitals) are
required for this system, making compromises on the size of RAS2 and/or the excitation level unavoidable, thus increasing the
uncertainty of the RASPT2 results by 0.1-0.2 eV. Still, also for this system, the RASPT2 method is shown to provide distinct
improvements over CASPT2, by overcoming the strict limitations in the size of the active space inherent to the latter method.
ISSN: 1549-9618
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Quantum Chemistry and Physical Chemistry Section
× corresponding author
# (joint) last author

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