Previously we predicted a strong wave-vector (q) dependence of the phonon linewidth for near-zone-center Raman phonons in YBa2Cu3O7 (C.O. Rodriguez, A.I. Liechtenstein, I.I. Mazin, O. Jepsen, O.K. Andersen, and M. Methfessel, Phys. Rev. B 42, 2692 (1990)). This prediction has now been qualitatively confirmed experimentally, and in order to make a quantitative comparison with experiments we have calculated the linewidths with higher accuracy on an expanded q scale. We find that the thresholds for the Landau damping of the Raman phonons agree very well with the experiments which indicates that the renormalization of the electron velocities at the Fermi level is small. The size of the linewidths, which depend on the electron masses, are, however, too small in the calculations. This discrepancy is possibly due to renormalization of the electron masses.
 

Physical Review B, 51 3961-4, 1995.