APW--LCAO band model for A15 compounds

The results of nonrelativistic augmented-plane-wave (APW) band-structure calculations at symmetry points in the cubic Brillouin zone for V3Si, V3Ge, Nb3Al, and Nb3Sn are fit using the Slater-Koster linear-combination-of-atomic-orbitals (LCAO) interpolation scheme. This LCAO model involves Bloch sums formed from 30 A-atom (A = V, Nb) d orbitals and eight B-atom (B = Si, Ge, Al, Sn) s-p orbitals. In its simplest form, this LCAO model fits 73 APW energy eigenvalues at GAMMA, X, M, and R with an rms error of 0.020 to 0.023 Ry by means of 21 two-center parameters. Improved accuracy is achieved, particularly for states near E/sub F/, by weighting these more heavily in the LCAO fit, partially relaxing the two-center approximation, and increasing the number of LCAO parameters to 39. The results of this APW-LCAO model are applied to evaluate the accuracy of the Labbe-Friedel (LF) linear-chain and the Weger-Goldberg (WG) coupled-chain band models for the A15 compounds. It is concluded that (a) corrections to the LF and WG models (about 3 and 1 eV, respectively) are sufficient to wash out fine structure in the density of states on a meV energy scale; (b) there is no evidence for describing the electronic structure of these A15 as one-dimensional or quasi-one-dimensional in character; (c) the density-of-states peak near E/sub F/ involves primarily A-atom d states with delta1(x2 - y2) symmetry, in contrast to the predictions of the LF (delta1 + delta2) and WG (delta2) models; (d) the accuracy of the present LCAO model is insufficient for predicting the precise shape of the density of states near E/sub F/ from first principles