Zero-field splitting in nickel(II) complexes: a comparison of DFT and multi-configurational wavefunction calculations

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Inorganic Chemistry

Background:

• Zero-field splitting (ZFS) is crucial for understanding electron spin Hamiltonians in systems with spin S = 1 or higher.
• Accurate ZFS prediction is essential for characterizing transition metal complexes.

Purpose of the Study:

• To calculate and compare the zero-field splitting (ZFS) in six- and five-coordinated nickel(II) complexes.
• To evaluate the performance of high-end ab initio methods versus various density functional theory (DFT) functionals for ZFS calculations.

Main Methods:

• Utilized the ORCA program package for theoretical calculations.
• Employed complete active space self-consistent field (CASSCF) and n-electron valence state perturbation theory (NEVPT2) with second-order and quasi-degenerate perturbation approaches.
• Compared ab initio results with DFT calculations using diverse functionals.

Main Results:

• Ab initio calculations provided consistent results that showed reasonable agreement with experimental data.
• Density functional theory (DFT) methods exhibited strong dependence on the chosen functional.
• DFT methods performed poorly for the studied nickel(II) complexes.

Conclusions:

• High-level ab initio methods are reliable for predicting ZFS in nickel(II) complexes.
• Standard DFT functionals are not suitable for accurate ZFS calculations in these systems.
• Further development of DFT functionals is needed for reliable ZFS prediction in similar coordination complexes.