Use of FLOSIC for understanding anion-solvent interactions.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Geochemistry

Background:

• Lower-rung density-functional approximations often fail to accurately describe anion electronic structures, exhibiting positive highest-occupied-molecular-orbital energy levels.
• The trianion [Cr(C2O4)3]3- is crucial for linking chromium isotope ratios in rocks to atmospheric oxygen levels over geological time.

Purpose of the Study:

• To apply crowd-sourced Fermi-Löwdin-Orbital-Self-Interaction corrected (FLOSIC) calculations to a complex trianion in solution.
• To address the self-interaction error prevalent in standard density-functional approximations for anionic systems.
• To enable accurate geochemical modeling involving chromium isotopes and atmospheric oxygen.

Main Methods:

• Utilized crowd-sourcing for self-consistent FLOSIC calculations on the [Cr(C2O4)3]3- trianion in water.
• Employed group-theory and sparsity for a 125-fold speedup in calculations compared to initial implementations.
• Analyzed core-level shifts of Cr and O atoms and integrated charge densities and Coulomb potentials.

Main Results:

• FLOSIC calculations provided a physically correct electronic structure for the trianion and surrounding water molecules.
• Uncorrected local density approximation (LDA) calculations showed significant, incorrect charge transfer from the anion to the water bath.
• FLOSIC calculations reversed the erroneous charge transfer observed with LDA and showed better agreement with experimental core ionization energies than other tested functionals.

Conclusions:

• FLOSIC calculations offer a robust solution to the self-interaction error in density-functional approximations for anionic systems.
• The developed computational approach accurately models the electronic structure of complex anions in solution, crucial for geochemical applications.
• This work validates the use of FLOSIC for precise modeling of chromium isotope behavior and its relation to Earth's atmospheric history.