Optical response of high temperature superconductors by full potential LAPW band structure calculations

Starting from selfconsistent full potential LAPW results we have investigated optical matrix elements for interband transitions and the ɛ ₂ tensor. These calculations are performed for YBa ₂Cu ₃O ₇ and YBa ₂Cu ₄O ₈. The spectra are analyzed and differences are discussed with respect to the crystal structures of the two systems. Our results are in good agreement with the ellipsometric determination of the dielectric function and previous LMTO calculations.