Full-potential linear-muffin-tin-orbital method for calculating total energies and forces

We present an efficient scheme for including full-potential terms in the linear-muffin-tin-orbital method. It is based on direct evaluation of the integrals in the interstitial region by partitioning crystalline space into atomic-cell envelopes and using one-center spherical harmonics expansions. This leads to a fast and accurate method for ab initio total-energy frozen-phonon calculations. The formulation for atomic forces is also given in this framework. Test results for phonon frequencies in a semiconductor, a transition metal, and a simple metal obtained from both the total-energy and force calculations are presented and found to be in good agreement with experiments.