First-principles theory of infrared vibrational spectroscopy in metals and semimetals: application to graphite

TL;DR

This paper presents an ab initio method based on density functional perturbation theory to accurately simulate infrared vibrational spectra of metals, exemplified by graphite, including complex Fano line shapes.

Contribution

The authors introduce a generalized frequency-dependent Born effective charge tensor within a first-principles framework to model IR spectra of metals, enabling detailed spectral predictions.

Findings

Successfully reproduces IR spectra of graphite

Describes phonon peaks with Fano functions influenced by electronic properties

Provides a new tool for high-pressure IR spectroscopy of metals

Abstract

We develop an ab initio method to simulate the infrared vibrational response of metallic systems in the framework of time-dependent density functional perturbation theory. By introducing a generalized frequency-dependent Born effective charge tensor, we show that phonon peaks in the reflectivity of metals can be always described by a Fano function, whose shape is determined by the complex nature of the frequency-dependent effective charges and electronic dielectric tensor. The IR vibrational properties of graphite, chosen as a representative test case to benchmark our method, are found to be accurately reproduced. Our approach offers a first-principle scheme for the prediction and understanding of IR reflectance spectra of metals, that may represent one of the few available tools of investigation of these materials when subjected to extremely high-pressure conditions.