Investigation of A1g phonons in YBa2Cu3O7 by means of LAPW atomic-force calculations (original) (raw)

We report first-principles frozen-phonon calculations for the determination of the force-free geometry and the dynamical matrix of the five Raman-active A 1g modes in YBa 2 Cu 3 O 7. To establish the shape of the phonon potentials atomic forces are calculated within the LAPW method. 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.