MAGNETIC-MOMENTS OF THE DIMERIC MULTIELECTRONIC MIXED-VALENCE CLUSTERS IN THE DYNAMIC-MODEL OF INTERMEDIATE VIBRONIC COUPLING

The vibronic problem of the pseudo-Jahn-Teller effect in multielectronic dimeric mixed valence clusters is discussed. The numerical diagonalization of the vibronic Hamiltonian is carried out using the intermediate coupling basis set. The temperature dependence of the magnetic moments of symmetric and distorted dimeric mixed valence clusters are derived. It is shown that vibronic coupling can suppress double exchange and lead to an antiferromagnetic ground state. Cases when the adiabatic approach leads to mistakes in describing of the ground state spin are discussed. It is shown that distortions of dimeric cluster which remove the inversion centre, lead to suppression of the ferromagnetic effect caused by double exchange.