  The physics of the Mott transition in the anodic region of NiO Resistance
Random Access Memory (RRAM) is discussed from the Hubbard model. The Hubbard
approximation is examined in details and it is shown that the Wannier functions
in the definition of Hubbard U should not be replaced by atomic s-functions
when it comes to the metallic side of the transition. The corresponding
effective Hubbard U is subject to variations, which may also be understood by
introducing an effective permittivity of the solid as an ansatz. Furthermore,
the transition could be demonstrated in the Brinkman-Rice picture. Finally, the
anodic characteristics of such transition show that it is a local Mott
transition. Therefore, the unipolar switching NiO RRAM can still have
asymmetric I-V curves when a capping layer is inserted, which is explained
qualitatively by quantum mechanics.
