Electronic structure and magnetism of Mn12O12 clusters

To address the ferrimagnetic state of the Mn-12 acetate matrix [Mn12O12(CH3 COO)(16)(H2O)(4)] we have performed all-electron gradient-corrected density -functional calculations on (MnO)(n) with n=1, 2, 4, and 12. In contrast to bulk MnO which is antiferromagnetic, the small (MnO)(n) (n = 1, 2, and 4) clusters are ferromagnetic with Mn moments of 5.0 mu(B) but the ground stat e of Mn12O12 is ferrimagnetic with a total magnetic moment of 20.0 mu(B) as observed experimentally. The inner Mn sites in Mn12O12 are found to have l ocalized moments of 4.1 mu(B) which are antiferromagnetically coupled to tw o types of outer Mn with moments of 4.2 mu(B) The cluster is shown to be ma rked by ionic as well as covalent bonds between Mn d and O p electrons and a strong intracluster magnetic coupling. [S0163-1829(99)51102-8].