Generalizedk→·p→interpolation method for electronic band structure: bcc iron

We have developed a series of $\overrightarrow{\mathrm{k}}$-dependent model band Hamiltonians in symmetrized polynomials, centered at points of high symmetry in the Brillouin zone, by means of local-group-invariant projectors - similar to the familiar Clebsh-Gordan coefficients of the full rotation group. We have tested these ideas by applying them to bcc iron. The results show that electronic structure is exponentially convergent in the expansion order of the polynomials: Expanding to fourth-order model energy bands fit Korringa-Kohn-Rostoker (KKR) bands to better than 2 mRy. For the bands of interest, the model scheme was more than 200 times faster than a fast KKR scheme.