Interatomic potentials for simulating MnO2 polymorphs

Interatomic potentials for manganese dioxide have been derived via fitting to the structures of the chain MnO2 polymorphs, pyrolucite and ramsdellite. The quality of the potentials was assessed by using them to simulate the structure of spinel-based lambda-MnO2 , which was not part of the fitting set. Lattice parameters of all three structures were reproduced to within 2% of the experimental values. The potentials have also been used to successfully simulate the idealised structures of the MnO2 polymorphs containing tunnels and suggest that tunnels larger than 2x3 are not stable without the presence of additional species within them. The stabilities of the polymorphs have been calculated and, somewhat unexpectedly, the spinel-based structure is found to be less stable that the tunnel structures.