Atomistic studies of energies and structures of (hk0) surfaces in NiO

Abstract

In this work we study the energies and structures of (hk0) surfaces in NiO by computer simulation. The short-range interactions are described by Buckingham potentials. The O ion is treated as polarizable by employing the shell model. The coefficients of the potentials and the shell parameters are fitted empirically to properties of the NiO perfect lattice assuming full ionicity. It is shown that discrete atomic structures of (hk0) surfaces can be treated as monatomic steps distributed uniformly or non-uniformly on {100} terraces. The energy of a surface is determined by the density of steps. The energy of the monatomic step is found to be 7·58 × 10 ⁻¹⁰Jm⁻¹ before relaxation and 3·32 × 10⁻¹⁰ Jm⁻¹ after relaxation. The elastic interaction between steps is repulsive and increases as the square of the step density. Surface rumpling is found to be a general property, with the anion cores moving outwards from the cations and also outwards from the anion shells, so that the anions are polarized. The polarization of anions decays as an exponential function of the distance from the surface, and the decay length ranges from 0·4a to 0·5a, where a is the lattice parameter. The change in the interlayer spacings and the movements of individual ions are investigated in detail.