Atomic and electronic structure and interatomic potentials at a polar ceramic/metal interface:{222}MgO/Cu

Abstract

Local density functional theory (LDFT) calculations, within the plane-wave-pseudopotential framework, are performed for the ${222}\mathrm{M}\mathrm{g}\mathrm{O}/\mathrm{C}\mathrm{u}$ polar interface, with the objective of elucidating the atomic and electronic structure of the interface, as well as interface interatomic potentials. Calculations are performed for both coherent interfaces and semicoherent interfaces that approximate the lattice constant mismatch of the true system. Calculations of local electronic density of states and adhesive energies are performed primarily for coherent interfaces. The density of electronic states at the interface for the oxygen-terminated configuration exhibits a peak in the bulk MgO energy gap that results from $\mathrm{O}(2p)\ensuremath{-}\mathrm{Cu}(3d)$ hybridization. The calculated interface adhesive energies for coherent interfaces as a function of the interface spacing and translation state are well reproduced by a simple analytical expression that combines an attractive Rydberg-function term and a repulsive pairwise Born-Mayer potential across the interface. Calculations are performed for a semicoherent interface with $5\ifmmode\times\else\texttimes\fi{}5\mathrm{Cu}$ layer unit cells opposite $4\ifmmode\times\else\texttimes\fi{}4$ MgO layer unit cells, an approximation to the true system with lattice constant ratio of 7/6, to investigate the relaxation at the interface in the presence of misfit. The terminating oxygen layer as well as the interface Cu layer exhibits warping albeit on a scale of less than 0.1 \AA{}.