Nanoscale Smoothing and the Analysis of Interfacial Charge and Dipolar Densities

TL;DR

This paper develops a theory of nanosmoothing for analyzing interfacial charge and dipole densities in multilayer materials, ensuring invariant results and improving the interpretation of first-principles electronic structure calculations.

Contribution

It introduces a rigorous nanosmoothing method that yields invariant interfacial charge and dipole densities, addressing limitations of heuristic approaches.

Findings

Nanosmoothing procedures can produce invariant interfacial charge and dipole densities.

Dipolar charge densities and screening lengths are not invariant under nanosmoothing.

The method is demonstrated using a toy model with Gaussian charge distributions.

Abstract

The interface properties of interest in multilayers include interfacial charge densities, dipole densities, band offsets, and screening-lengths, among others. Most such properties are inaccesible to direct measurements, but are key to understanding the physics of the multilayers. They are contained within first-principles electronic structure computations but are buried within the vast amount of quantitative information those computations generate. Thus far, they have been extracted from the numerical data by heuristic nanosmoothing procedures which do not necessarily provide results independent of the smoothing process. In the present paper we develop the theory of nanosmoothing, establishing procedures for both unpolarized and polarized systems which yield interfacial charge and dipole densities and band offsets invariant to the details of the smoothing procedures when the criteria we have established are met. We show also that dipolar charge densities, i. e. the densities of charge transferred across the interface, and screening lengths are not invariant. We illustrate our procedure with a toy model in which real, transversely averaged charge densities are replaced by sums of Gaussians.