DENSITY-FUNCTIONAL PERTURBATION-THEORY FOR LATTICE-DYNAMICS WITH ULTRASOFT PSEUDOPOTENTIALS

We generalize density-functional perturbation theory for lattice dynam ics to Vanderbilt's ultrasoft pseudopotential scheme. This formulation accounts for the nonorthogonality of the orbitals, the augmentation o f the electron density, and the dependence of the generalized orthogon ality constraint on the atomic positions. Both insulating and metallic systems are considered. Application of the theory to the vibrations o f small molecules (CO, CO2, CH4, and H2O) and to the phonon dispersion of the noble metals (Cu, Ag, Au) shows overall agreement with experim ent. [SO163-1829(97)51742-5].