Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Effect of Geometry, Spin and Orbital Optimization in Achieving
  Accurate, Fully-Correlated Results for Iron-Sulfur Cubanes   Iron-sulfur clusters comprise an important functional motif of 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
fully-correlated 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
cubane-based clusters using two complementary, fully-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 lowest singlet and the highest spin
states is strongly geometry dependent, changing by an order of magnitude 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 by a factor of two
compared to typical mean-field orbital approaches. Our results clearly
demonstrate the need for performing highly correlated calculations to unveil
the challenging electronic structure of these complex catalytic centers.

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The categories of this paper are: math
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The categories of this paper are: dg-ga
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The categories of this paper are: comp-gas
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The categories of this paper are: atom-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-ex
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-ph
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The categories of this paper are: stat
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The categories of this paper are: patt-sol
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The categories of this paper are: q-bio
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The categories of this paper are: solv-int
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The categories of this paper are: chao-dyn
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The categories of this paper are: econ
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The categories of this paper are: acc-phys