@article{10.1103PhysRev.52.191,
  author = {Wannier, Gregory H.},
  doi = {10.1103/PhysRev.52.191},
  issue = {3},
  journal = {Physical Review},
  month = {8},
  pages = {191--197},
  title = {The Structure of Electronic Excitation Levels in Insulating Crystals},
  type = {article},
  url = {http://link.aps.org/article/10.1103/PhysRev.52.191},
  volume = {52},
  year = {1937},
}
