Analysis of the magnetic coupling in binuclear complexes. I. Physics of the coupling

Abstract

Accurate estimates of the magnetic coupling in binuclear complexes can be obtained from ab initio configuration interaction ͑CI͒ calculations using the difference dedicated CI technique. The present paper shows that the same technique also provides a way to analyze the various physical contributions to the coupling and performs numerical analysis of their respective roles on four binuclear complexes of Cu (d 9 ) ions. The bare valence-only description ͑including direct and kinetic exchange͒ does not result in meaningful values. The spin-polarization phenomenon cannot be neglected, its sign and amplitude depend on the system. The two leading dynamical correlation effects have an antiferromagnetic character. The first one goes through the dynamical polarization of the environment in the ionic valence bond forms ͑i.e., the M ϩ¯MϪ structures͒. The second one is due to the double excitations involving simultaneously single excitations between the bridging ligand and the magnetic orbitals and single excitations of the environment. This dispersive effect results in an increase of the effective hopping integral between the magnetic orbitals. Moreover, it is demonstrated to be responsible for the previously observed larger metal-ligand delocalization occurring in natural orbitals with respect to the Hartree-Fock ones.

Spin-orbit effects in heavy-atom organic radical ferromagnets

“…2. 17 This configuration affords two charge transfer singlet states S (+) (in-phase) and S (−) (out-of-phase), an openshell singlet state S (0) and a triplet manifold {T }. The effect of the on-site Coulomb potential is to increase the energy of the charge transfer states by U with respect to the open-shell states.…”

Analysis of the magnetic coupling in binuclear systems. III. The role of the ligand to metal charge transfer excitations revisited

“…[20][21][22][23][24][25][26][27][28][29][30][31][32] Some years ago we took benefit of this methodology to analyze in depth the physical contributions to the magnetic coupling on a series of binuclear Cu ͑II͒ complexes. 33 The use of the DDCI strategy allows not only to obtain quite accurate J values but also to analyze the various physical effects by generating CI spaces of increasing lengths that include different types of determinants. We also reported a procedure to define valence effective Hamiltonians starting from the eigenenergies and eigenvectors of these CI calculations.…”

A convenient decontraction procedure of internally contracted state-specific multireference algorithms

“…The case of the binuclear magnetic complexes, where the ionic VB component of the singlet state is grossly underestimated at the valence CAS level, is a well documented example. 36,68 The paper has proposed a state-specific decontraction procedure for state-specific MR algorithms. It is based on the use of slightly perturbed zero-order wave functions.…”