C. Troestler et M. Willem, NONTRIVIAL SOLUTION OF A SEMILINEAR SCHRODINGER-EQUATION, Communications in partial differential equations, 21(9-10), 1996, pp. 1431-1449
This paper deals with strongly indefinite functionals whose gradients
are Fredholm operators of index 0 and map weakly convergent sequences
to weakly convergent sequences. We show bow these results apply to a Z
(N)-invariant semilinear Schrodinger equation on R(N).