First-principles calculations of charged surfaces and interfaces: A plane-wave nonrepeated slab approach

A new first-principles computational approach to a charged surface/interface is presented. The surface is modeled as a slab imposed with boundary conditions to screen the excess surface charge. To treat this model, which is nonperiodic in the surface normal direction, a standard pseudopotential plane-wave scheme is modified at the Poisson solver part with the help of the Green's function technique. Benchmark calculations are done for Al/Si(111) with the bias voltage applied between the surface and the model scanning tunneling microscopy (STM) tip, the model back gate, or the model solution. The calculations are found to be efficient and stable, and their implementation is found to be easy. Because of the flexibility, the scheme is considered to be applicable to more general experimental situations.