@article{10_4171_dm_150,
     author = {Rupert L. Frank},
     title = {On the scattering theory of the {Laplacian} with a periodic boundary condition. {I.} {Existence} of wave operators},
     journal = {Documenta mathematica},
     pages = {547--565},
     year = {2003},
     volume = {8},
     doi = {10.4171/dm/150},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/dm/150/}
}