The Effect of Geometry, Spin, and Orbital Optimization in Achieving Accurate, Correlated Results for Iron-Sulfur Cubanes

0552754 - ÚFCH JH 2023 RIV US eng J - Journal Article
Mejuto-Zaera, C. - Tzeli, D. - Williams-Young, D. B. - Tubman, N. - Matoušek, Mikuláš - Brabec, Jiří - Veis, Libor - Xantheas, S. - de Jong, W. A.
The Effect of Geometry, Spin, and Orbital Optimization in Achieving Accurate, Correlated Results for Iron-Sulfur Cubanes.
Journal of Chemical Theory and Computation. Roč. 18, č. 2 (2022), s. 687-702. ISSN 1549-9618. E-ISSN 1549-9626
R&D Projects: GA ČR(CZ) GJ18-18940Y
Research Infrastructure: IT4Innovations - 90070
Institutional support: RVO:61388955
Keywords : matrix renormalization-group * density-functional theory * electronic-structure * quantum-theory * ab-initio * photoelectron-spectroscopy * configuration-interaction * cluster biosynthesis * angstrom resolution * synthetic analogs
OECD category: Physical chemistry
Impact factor: 5.5, year: 2022
Method of publishing: Limited access

Iron-sulfur clusters comprise an important functional motif in the catalytic centers of biological systems, capable of enabling important chemical transformations at ambient conditions. This remarkable capability derives from a notoriously complex electronic structure that is characterized by a high density of states that is sensitive to geometric changes. The spectral sensitivity to subtle geometric changes has received little attention from correlated, large active space calculations, owing partly to the exceptional computational complexity for treating these large and correlated systems accurately. To provide insight into this aspect, we report the first Complete Active Space Self Consistent Field (CASSCF) calculations for different geometries of the [Fe(II/III)(4)S-4(SMe)(4)](-2) clusters using two complementary, correlated solvers: spin-pure Adaptive Sampling Configuration Interaction (ASCI) and Density Matrix Renormalization Group (DMRG). We find that the previously established picture of a double-exchange driven magnetic structure, with minute energy gaps (<1 mHa) between consecutive spin states, has a weak dependence on the underlying geometry. However, the spin gap between the singlet and the spin state 2S + 1 = 19, corresponding to a maximal number of Fe-d electrons being unpaired and of parallel spin, is strongly geometry dependent, changing by a factor of 3 upon slight deformations that are still within biologically relevant parameters. The CASSCF orbital optimization procedure, using active spaces as large as 86 electrons in 52 orbitals, was found to reduce this gap compared to typical mean-field orbital approaches. Our results show the need for performing large active space calculations to unveil the challenging electronic structure of these complex catalytic centers and should serve as accurate starting points for fully correlated treatments upon inclusion of dynamical correlation outside the active space.
Permanent Link: http://hdl.handle.net/11104/0327863