Wavevector-dependent optical properties from wavevector-independent proper conductivity tensor

TL;DR

This paper examines the calculation of optical properties using a microscopic dielectric tensor, addressing limitations of traditional methods and clarifying the relation between fundamental and standard wave equations in optics.

Contribution

It introduces a framework based on a wavevector-dependent dielectric tensor to improve the calculation of optical properties from ab initio data.

Findings

Identifies limitations of scalar dielectric function in refractive index calculations.

Establishes conditions under which the microscopic wave equation aligns with standard optics.

Clarifies the relation between microscopic and effective dielectric tensors.

Abstract

We discuss the calculation of the refractive index by means of the ab initio scalar dielectric function and point out its inherent limitations. To overcome these, we start from the recently proposed fundamental, microscopic wave equation in materials in terms of the frequency- and wavevector-dependent dielectric tensor, and investigate under which conditions the standard treatment can be justified. Thereby, we address the question of neglecting the wavelength dependence of microscopic response functions. Furthermore, we analyze in how far the fundamental, microscopic wave equation is equivalent to the standard wave equation used in theoretical optics. In particular, we clarify the relation of the "effective" dielectric tensor used there to the microscopic dielectric tensor defined in ab initio physics.