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 provi de 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 n et 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 th e sign and magnitude of the overlap population, suggests strong covale ncy in this system in terms of p-d hybridisation.