First-principles description of the valence charge states in rutile MnO₂

First-principles periodic Hartree-Fock calculations of the ground and first ionised and electron-addition states of rutile MnO2 are reported from which the integrated charge-and spin-density distributions provide direct evidence that the charge state of Mn is essentially d(5), as it is in MnO, and remains so with electron removal or addition. The net spin moment on Mn, on the other hand, is ca. 3 mu(B), which is that normally associated with the Mn-IV valence state, indicating that the unpaired d(5) electron density is delocalised. This, together with the sign and magnitude of the overlap population, suggests strong covalency in this system in terms of p-d hybridisation.