A method for calculating both the valence- and high-lying conduction-band structure of a solid is developed. The basis functions are linear-muffin-tin orbitals with multiple orbitals per angular momentum channel corresponding to different energies. In contrast to the conventional paneling method, our method treats the valence and conduction bands on an equal footing so that the wave functions are orthogonal, which avoids the nonorthogonality problem when calculating transition-matrix elements between occupied and unoccupied states and the discontinuity in the band structure. An empty-lattice test reproduces the free-electron band up to at least 50 eV. The method is applied to nickel and a comparison with a different approach based on a modified linear augmented-planewave method is made.
 

Physical Review B, 49 7219-32, 1994.