@incollection{AST_1992__210__135_0,
     author = {Helffer, B. and Sj\"ostrand, J.},
     title = {Semiclassical expansions of the thermodynamic limit for a {Schr\"odinger} equation},
     booktitle = {M\'ethodes semi-classiques Volume 2 - Colloque international (Nantes, juin 1991)},
     series = {Ast\'erisque},
     pages = {135--181},
     publisher = {Soci\'et\'e math\'ematique de France},
     number = {210},
     year = {1992},
     language = {en},
     url = {http://www.numdam.org/item/AST_1992__210__135_0/}
}