Ab initio Hartree-Fock investigation of the structural, electronic, and magnetic properties of Mn3O4

Noncubic Mn3O4 spinel (Hausmannite) has been investigated by using the peri odic Hartree-Fock CRYSTAL95 program. The structure has been fully optimized , and the computed geometry compares well with the experimental data. The a nalysis of the wave function in terms of Mulliken charges shows that the ne t charge of the tetrahedral cation (Mn-A) is very close to the formal one ( +1.86 electrons to be compared to +2); for the octahedral site (Mn-B) the n et charge is far from the ideal ionic model (+2.3 electrons instead of +3), and the Mn-B-O bonds show some covalent character. The same analysis perfo rmed on the spin density gives magnetic moments very close to the ones corr esponding to the ideal d(4) and d(5) configurations (4.90 and 3.97 electron s for Mn-A and Mn-B, respectively). The total energy of seven different spi n configurations has been evaluated and the corresponding wave function ana lyzed. Superexchange coupling constants are evaluated by mapping the ab ini tio energy data to the Ising hamiltonian. It turns out that the intertetrah edral and tetrahedral-octahedral magnetic interactions are small and antife rromagnetic, in agreement with experimental evidence. The Mn-B-Mn-B alone t he octahedra chains is ten times larger, whereas the interchain interaction is small and ferromagnetic. [S0163-1829(99)03843-6].