First-principles Raman studies on rare-earth carbide halides

We have investigated the zone-center Raman modes of Y2C2Br2 and Y2C2I2 by f irst-principles calculations based on density functional theory. The phonon frequencies are determined by carrying out total-energy and atomic-force c alculations using the full-potential linearized augmented plane-wave (LAPW) method. The Raman intensities are obtained from the derivative of the diel ectric function with respect to the normal coordinates of the phonons. We f ind excellent agreement with previously measured Raman spectra.