On The Influence of Two Parallel Plates on Atomic Levels
  This paper is devoted to the study of the influence of two parallel plates on the atomic levels of a Hydrogen atom placed in the region between the plates. We treat two situations, namely: the case where both plates are infinitely permeable and the case where one of them is a perfectly conducting plate and the other, an infinitely permeable one. We compare our result with those found in literature for two parallel conducting plates. The limiting cases where the atom is near a conducting plate and near a permeable one are also taken. 
D. T. Alves, F. A. Barone, C. Farina, A. C. Tort