Response Functions and Density of States

Abstract

The experimental input to the EPM is achieved through a comparison of measured and calculated spectra. Only a few pseudopotential form factors are required to determine accurate energy eigenvalues and wavefunctions. The method requires a calculation of a response function to compare with experimental data. Two major sources of measured spectra are optical reflectivity and photoemission data for the energy distribution curves (EDC) of the emitted electrons. The reflectivity spectra can be analyzed in terms of a frequency-dependent complex dielectric function, while the photoemission EDC can be compared with calculated density of states curves. The details and methods regarding the use of the measured spectra will be discussed elsewhere in this volume. Here we describe the theoretical calculations of the response functions.