Analytic continuation of the dynamic response function using an N-point Pade approximant

Abstract

We use the N-point Pade approximant to make the analytic continuation of the dynamic response function. This continuation scheme reproduces very efficiently the plasmon energy dispersion and the dynamic scattering cross section with double peaks for Al. For Si with covalent bondings, the energy-loss function exhibits the anomalous feature in the long-wavelength limit, which was also found in previous work. At large wave vectors, the local-field effect shifts the plasmon excitation peak to higher energy, however, this shift is compensated by the exchange-correlation effect.