Exactk-qsolution for a Bloch electron in a constant electric field

In a series of recent papers, a new method for exactly solving the Schr\"odinger equation for a single electron in a crystal subjected to a constant, external, electric field (Wannier-Stark problem) has been presented. In the present report, the k-q representation of J. Zak [Phys. Rev. 168, 686 (1968)] is shown to give exactly these same results.