Peschel, I. Max Planck Institute for the Physics of Complex Systems, Max Planck Society;
http://arxiv.org/pdf/cond-mat/9406047.pdf (Preprint)
Peschel, I., Rittenberg, V., & Schultze, U. (1994). Spectra of quantum chains without the Yang-Baxter equation. Nuclear Physics B, 430, 633-655.