First-principles calculations of phonon dispersion and lattice dynamics inLa2CuO4

First-principles density-functional linearized augmented plane-wave linear- response calculations are presented of the lattice dynamics of tetragonal L a2CuO4. Phonon frequencies and eigenvectors are obtained throughout the Bri llouin zone. Generally good agreement is achieved with experiment, but freq uencies of the lowest-lying branches, which involve anharmonic motion of th e epical oxygen atoms parallel to the CuO2 planes, are underestimated. The octahedral tilt mode at the X point is found to be the most unstable mode t hroughout the Brillouin zone, consistent with the observed phase transition to the orthorhombic structure at low temperature. The calculated dispersio n of the highest frequency Sigma(3) branch is in good agreement with experi ment, showing that a proposed large renormalization of the phonon spectrum by a Jahn-Teller electron-phonon interaction is unlikely. [S0163-1829(99)12 513-X].