Investigation of A1g phonons in YBa2Cu3O7 by means of LAPW atomic–force calculations

We report first–principles frozen–phonon calculations for the determination of the force–free geometry and the dynamical matrix of the five Raman–active A1g modes in YBa2Cu3O7. To establish the shape of the phonon potentials atomic forces are calculated within the LAPWmethod. Two different schemes – the local density approximation (LDA) and a generalized gradient approximation (GGA) – are employed for the treatment of electronic exchange and correlation effects. We find that in the case of LDA the resulting phonon frequencies show a deviation from experimental values of approximately -10%. Invoking GGA the frequency values are significantly improved and also the eigenvectors are in very good agreement with experimental findings. Typeset using REVTEX