All-electron and pseudopotential force calculations using the linearized-augmented-plane-wave method

All-electron and pseudopotential formulations for atomic forces in the linear-augmented-plane-wave (LAPW) method within the local-density approximation are presented. Due to the fact that the basis functions in the LAPW method (and in other linear muffin-tin-orbitals-based methods) have discontinuous second derivatives across the muffin-tin sphere boundaries, a large surface contribution to the incomplete-basis-set corrections to the Hellmann-Feynman force is shown to exist. The formulations are applied to frozen-phonon calculations in semiconductor, transition-metal, and noble-metal systems. The results are in excellent agreement with total-energy calculations and experiment.