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

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