High-throughput
searches for spin-crossover molecules require Hubbard-U corrections to common density functional exchange-correlation
(XC) approximations. However, the U
eff
values obtained from linear response or based on previous
studies overcorrect the spin-crossover energies. We demonstrate that
employing a linearly mixed ensemble average spin state as the reference
configuration for the linear response calculation of U
eff
resolves this issue. Validation on
a commonly used set of spin-crossover complexes shows that these ensemble U
eff
values consistently are
smaller than those calculated directly on a pure spin state, irrespective
of whether that be low- or high-spin. Adiabatic crossover energies
using this methodology for a generalized gradient approximation XC
functional are closer to the expected target energy range than with
conventional U
eff
values.
Based on the observation that the U
eff
correction is similar for different complexes that share transition
metals with the same oxidation state, we devise a set of recommended
averaged U
eff
values
for high-throughput calculations.
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