The role of dynamical polarization of the ligand to metal charge transfer excitations in {\em ab initio} determination of effective exchange parameters

TL;DR

This paper investigates how ligand-to-metal charge transfer excitations influence magnetic coupling constants and introduces a computationally efficient variant of the DDCI method that accurately accounts for these effects.

Contribution

A new variant of the DDCI method is proposed, explicitly treating ligand orbitals mediating magnetic interactions, reducing computational cost while maintaining high accuracy.

Findings

Ligand-to-metal charge transfer excitations significantly impact magnetic coupling constants.

The new DDCI variant achieves accurate results with a reduced configuration space.

The method enables studies of more complex magnetic systems.

Abstract

The role of the bridging ligand on the effective Heisenberg coupling parameters is analyzed in detail. This analysis strongly suggests that the ligand-to-metal charge transfer excitations are responsible for a large part of the final value of the magnetic coupling constant. This permits to suggest a new variant of the Difference Dedicated Configuration Interaction (DDCI) method, presently one of the most accurate and reliable for the evaluation of magnetic effective interactions. This new method treats the bridging ligand orbitals mediating the interaction at the same level than the magnetic orbitals and preserves the high quality of the DDCI results while being much less computationally demanding. The numerical accuracy of the new approach is illustrated on various systems with one or two magnetic electrons per magnetic center. The fact that accurate results can be obtained using a rather reduced configuration interaction space opens the possibility to study more complex systems with many magnetic centers and/or many electrons per center.