INVESTIGATION OF A(1G) PHONONS IN YBA2CU3O7 BY MEANS OF LINEARIZED-ANGMENTED-PLANE-WAVE ATOMIC-FORCE CALCULATIONS

We report first-principles frozen-phonon calculations for the determin ation of the force-free geometry and the dynamical matrix of the five Raman-active A(1g) modes in YBa2Cu3O7. To establish the shape of the p honon potentials atomic forces are calculated within the linearized-au gmented-plane-wave method. Two different schemes-the local-density app roximation (LDA) and a generalized, gradient approximation (GGA)-are e mployed for the treatment of electronic exchange and correlation effec ts. We find that in the case of LDA the resulting phonon frequencies s how a deviation from experimental values of approximately -10%. Invoki ng GGA the frequency values are significantly improved and also the ei genvectors are in very good agreement with experimental findings.