Al. Tchougreeff et al., HIGH-SPIN LOW-SPIN TRANSITIONS IN FE(II) COMPLEXES BY EFFECTIVE HAMILTONIAN METHOD, Chemical physics, 193(1-2), 1995, pp. 19-26
The high-spin-low-spin (HS-LS) transition in iron(II) complexes was st
udied by the recently developed quantum chemical effective Hamiltonian
method. This method uses a trial wave function which is an antisymmet
rized product of the fully correlated function of d-electrons and of t
he Slater determinant of the ligand MOs instead of the conventional Ha
rtree-Fock single determinant trial wave function built of the molecul
ar orbitals spread over an entire complex. This approach allowed us to
explicitly take into account the d-electron correlations, the weak co
valence of the metal-ligand bonds, and the electronic structure of the
ligands. The cooperativity effects in the HS-LS transition occurring
in the crystals are briefly discussed and the contribution from the Co
ulomb forces to the intermolecular interaction responsible for the coo
perativity is estimated.