Mean Value Ensemble Hubbard-U Correction for Spin-Crossover Molecules.

Area of Science:

• Computational Chemistry
• Materials Science
• Quantum Chemistry

Background:

• High-throughput screening of spin-crossover (SCO) molecules necessitates accurate electronic structure calculations.
• Common density functional approximations often require Hubbard U corrections for accurate modeling of SCO phenomena.
• Existing methods for determining U values, such as linear response on pure spin states, can lead to overcorrection of SCO energies.

Purpose of the Study:

• To develop a more accurate method for calculating Hubbard U values for spin-crossover molecules.
• To improve the accuracy of spin-crossover energy calculations in high-throughput screening.
• To establish a set of recommended averaged U values for practical applications.

Main Methods:

• Utilized a linearly mixed ensemble average spin state as the reference configuration for linear response calculations of U.
• Validated the proposed method on a standard set of spin-crossover complexes.
• Employed a generalized gradient approximation (GGA) exchange-correlation functional.

Main Results:

• Ensemble-averaged U values were consistently smaller than those calculated from pure spin states (low- or high-spin).
• Adiabatic crossover energies calculated with the ensemble U method were closer to the expected target energy range.
• Identified similar U corrections for complexes with the same transition metal and oxidation state.

Conclusions:

• The ensemble average spin state approach effectively resolves the overcorrection issue in Hubbard U calculations for SCO.
• This methodology provides more accurate adiabatic crossover energies compared to conventional U values.
• A set of recommended averaged U values is proposed for efficient high-throughput SCO calculations.