Alternative Augmented-Plane-Wave Technique: Theory and Application to Copper

An alternative augmented-plane-wave (APW) method based on the matching of both the function and derivative across the APW sphere boundary is presented. This matching is accomplished by expanding the basis function inside the sphere using two sets of functions for each $l$: One set consists of the solutions with zero derivative, and the other of those with zero value at the APW sphere surface. The method is then applied to the Chodorow copper potential as a test case. In addition, the relativistic formulation and the extension to include non-muffin-tin potential terms are presented.